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A  PRACTICAL   COURSE    IN 
BOTANY 

WITH   ESPECIAL   REFERENCE   TO   ITS    BEARINGS   ON 
AGRICULTURE,  ECONOMICS,  AND  SANITATION 


BY 
E.    F.  ANDREWS 

AUTHdK    OF    "  BOTANV    ALL    THE    VKAK    ROUND" 

WITH   EDITORIAL   REVISION   BY 

FRANCIS    E.    LLOYD 

MACDONALI)    PROFESSOR    OF    BOTANV,    MCGILL    UNIVERSITY, 
FORMKRLV    OF    ALABAMA    HOI.VTECllNIC    INSTITUTE 


NEW   YORK    •:■    CINCINNATI    ■:      CHICAGO 

AMERICAN    BOOK    COMPANY 


Copyright,  1911,  by 
E.   F.   ANDREWS. 

Entehed  at  Stationers'  Hall,  London, 

andkews's  i'r.  botany. 
w.  p.    7 


b^Vx 


^^^ 


K^ 


PREFACE 


In  preparing  the  present  volume,  the  aim  of  the  writer  has 
been  to  meet  all  the  college  entrance  requirements  and  at  the 
same  time  to  bring  the  stud}'  of  botany  into  closer  touch  with 
the  practical  business  of  life  by  stressing  its  relations  with 
agriculture,  economics,  and,  in  certain  of  its  aspects,  with  sani- 
tation. While  technical  language  has  been  avoided  so  far 
as  the  requirements  of  scientific  accuracy  will  permit,  the 
student  is  not  encouraged  to  shirk  the  use  of  necessary  botani- 
cal terms,  out  of  a  mere  superstitious  fear  of  words  because 
they  happen  to  be  a  little  new  or  unfamiliar.  Such  a  practice 
not  only  leads  to  careless  and  inaccurate  modes  of  expression, 
but  tends  to  foster  a  slovenly  habit  of  mind,  and  in  the  long  run 
causes  the  waste  of  more  time  and  labor  in  the  search  after 
roundabout,  and  often  misleading,  substitutes,  than  it  would 
require  to  master  the  proper  use  of  a  few  new  words  and 
phrases. 

In  the  choice  of  materials  for  experiment  and  illustration, 
the  endeavor  has  been  to  call  for  such  only  as  are  familiar  and 
easily  obtained.  The  specimens  for  flower  dissection  have  been 
selected  mainly  from  common  cultivated  kinds,  because  their 
wide  distribution  makes  them  easy  to  obtain  everywhere,  while 
in  cities  and  large  towns  they  are  practically  the  only  specimens 
available.  Another  important  consideration  has  been  the  desire 
to  spare  our  native  wild  flowers,  or  at  least  not  to  hasten  the 
extinction  with  which  they  are  threatened  by  the  ravages  of  Sun- 
day excursionists  and  summer  tourists,  to  whose  unthinking, 
but  none  the  less  destructive,  incursions,  the  automobile  has  laid 
open  the  most  secret  haunts  of  nature.  The  influence  of  the 
public  school  teacher,  and  more  especially  the  teacher  of  botany, 
is  the  most  potent  factor  from  which  we  can  hope  for  aid  in 
putting  a  stop  to  the  relentless  persecution  that  has  practically 
exterminated   many  of   our   choicest  wild   plants  and  is  fast 


7/77 


*^^  9^' COLLEGE  UBRm, 


IV  PREFACE 

reducing  the  civilized  world  to  a  depressing  monotony  of 
weediness  and  artificiality.  Except  for  purely  systematic  and 
anatomical  work,  flowers  can  be  studied  to  better  put  pose  in 
their  living,  active  state  than  as  dead  subjects  for  dissection ; 
and  the  best  way  to  show  our  interest  in  them,  or  to  get  the 
most  rational  enjoyment  out  of  them,  is  not,  as  a  general  thing, 
to  cut  their  heads  off  and  throw  them  away  to  wither  and  die 
by  the  roadside.  The  teacher,  by  instilling  into  the  minds  of 
the  rising  generation  a  reverence  for  plant  life,  may  do  a  great 
deal  to  aid  in  the  conservation  of  one  of  our  chief  national  assets 
for  the  gratification  of  the  higher  esthetic  instincts.  The  fruits 
and  flowers  of  cultivation  do  not  stand  in  the  same  need  of  pro- 
tection, since  they  are  produced  solely  with  a  view  to  the  use 
and  pleasure  of  man,  and  their  propagation  is  provided  for  to 
meet  all  his  demands. 

To  avoid  too  frequent  interruptions  of  the  subject  matter, 
the  experiments  are  grouped  together  at  the  beginning  or  end 
of  the  sections  to  which  they  belong,  according  as  they  are 
intended  to  explain  what  is  coming,  or  to  illustrate  what  has 
gone  before.  A  few  exceptions  are  made  in  cases  where  the 
experiment  is  such  an  integral  part  of  the  subject  that  it  would 
be  meaningless  if  separated  from  the  context.  Under  no 
circumstances  should  those  capable  of  being  performed  in  the 
schoolroom  be  omitted,  as  much  of  the  information  which  the 
book  is  intended  to  give  is  conveyed  by  their  means.  For  this 
reason,  and  also  because  the  aim  of  the  book  is  to  present  the 
science  from  a  practical  rather  than  from  an  academic  point  of 
view,  the  experiments  outlined  are  for  the  most  part  of  a  simple, 
practical  nature,  such  as  can  be  performed  by  the  pupils  them- 
selves with  a  moderate  expenditure  of  ingenuity  and  money. 
The  experience  of  the  writer  has  been  that  for  the  average  boy 
or  girl  who  wishes  to  get  a  good  general  knowledge  of  the 
subject,  but  does  not  i3ropose  to  become  a  specialist  in  botany, 
the  best  results  are  often  obtained  by  the  use  of  the  simplest 
and  most  familiar  appliances,  as  in  this  way  attention  is  not 
distracted  from  the  experiment  itself  to  the  unfamiliar  appa* 
ratus  for  making  it.     In  saying  this,  it  is  not  meant  to  under- 


PREFACE  V 

rate  the  value  of  a  complete  laboratory  equipment,  but  merely 
to  emphasize  the  fact  that  the  lack  of  it,  while  a  disadvantage, 
need  Jiot  be  an  insuperable  bar  to  the  successful  teaching  of 
botany.  It  is,  of  course,  taken  for  granted  that  in  schools  pro- 
vided with  a  suitable  laboratory  outfit,  teachers  will  be  pre- 
pared to  supplement  or  to  replace  the  exercises  here  outlined 
with  such  others  as  in  their  judgment  the  subject  may  demand. 
There  are  as  many  ideals  in  teaching  as  there  are  teachers,  and 
the  most  that  a  textbook  can  do  is  to  present  a  working  model 
which  every  teacher  is  free  to  modify  in  accordance  with  his 
or  her  own  method. 

The  writer  takes  pleasure  in  acknowledging  here  the  many 
obligations  due  to  Professor  Francis  E.  Lloyd,  of  the  Botanical 
Department  of  the  Alabama  Polytechnic  Institute,  at  Auburn, 
Ala.,  for  his  valuable  aid  in  the  revision  of  the  manuscript,  for 
the  highly  interesting  series  of  illustrations  relating  to  photo- 
tropic  movements,  and  for  advice  and  information  on  points 
demanding  expert  knowledge  which  have  contributed  very  ma- 
terially to  whatever  merit  this  volume  may  possess. 

Other  members  of  the  Auburn  faculty  to  whom  the  author 
feels  especially  indebted  are  Mr.  C.  S.  Ridgeway,  assistant  in  the 
Botanical  Department,  Professor  J.  E.  Duggar,  of  the  Agricul- 
tural Department,  and  Dr.  B.  B.  Ross  and  Professor  C.  W. 
Williamson  of  the  Department  of  Chemistry.  Acknowledg- 
ments are  due  also  to  Professor  George  Wood  of  the  Boys'  High 
School,  Brooklyn,  for  suggestions  which  have  been  of  great 
assistance  in  the  preparation  of  this  work ;  to  Professor  W.  R. 
Dodson,  of  the  University  of  Louisiana,  for  illustrative  material 
furnished,  and  to  Professor  William  Trelease  for  tlie  loan  of 
original  material  used  in  reproducing  the  beautiful  cuts  from 
the  Reports  of  the  Missouri  Botanical  Garden,  credit  for  which 
is  given  in  the  proper  place. 

For  original  photographs  and  drawings  by  the  author,  and 
familiar  selections  from  well-known  works,  which  can  be  gen- 
erally recognized,  it  has  not  been  thought  necessary  to  give 

special  credit. 

E.   F.   ANDREWS. 
Auburn,  Alabama. 


FULL-PAGE   ILLUSTRATIONS 

PLATE  PAOiE 

1.  A  GROVE  OF  LIVE  OAKS  NEAR  SAVANNAH,  GEORGIA  .         Frontispiece 

2.  Carrying  water  over  the  Mississippi  levee  by  siphon  to 

irrigate  rice  fields 8 

3.  Aerial  roots  of  a  Mexican  strangling  fig          ...  73 

4.  A  forest  of  bamboo 99 

5.  A  group  of  conifers 108 

6.  A    WHITE    OAK,    showing    THE    GREAT    SPREAD    OF    BRANCHES           .  117 

7.  a  timber  tree  spoiled  by  standing  too  much  alone          .  125 

8.  An  American  elm,  illustrating  deliquescent  growth       .  130 

9.  Vegetation  of  a  moist,  shady  ravine 151 

10.  A  MOSAIC  OF  moonseed  leaves 179 

11.  Hybrid  between  a  red  and  a  white  carnation  .        .        .  227 

12.  Gooseberries,  showing  improvement  by  selection       .        .  251 

13.  The  effects  of  irrigation 272 

14.  A  xerophyte  formation  of  yuccas  and  switch  plants       .  282 

15.  A  giant  tulip  tree  of  the  South  Atlantic  forest  region  298 


CONTENTS 


CHAPTER   I.     THE   SEED 


I.     The  Storage  of  Food  in  Seeds 
11.     Some  Physiological  Properties  ok  Seeds 

III.  Types  of  Seeds 

IV.  Seed  Dispersal 

Field  Work 


PAGE 
1 

10 
12 
21 

28 


CHAPTER  11.  GEKMIXATIOX  AND  GROWTH 


I.     Processes  accompanying  Germination 
n.     Conditions  of  Germination 

III.  Development  of  the  Seedling 

IV.  Growth 

Field  AVork  


CHAPTER  ni.     THE   ROOT 

I.  Osmosis  and  the  Action  of  the  Cell   . 

11.  jMineral  Nutriments  absorbed  by  Plants 

III.  Structure  of  the  Root     .... 

IV.  The  AVork  of  Roots 

V.  Different  Forms  of  Roots 

Field  AVork  


•CHAPTER  lA^     THE   STEM 


I.     Forms  and  Growth  of  Stems  . 
II.     Modifications  of  the  Stem 
in.     Stem  Structure 

A.  MoNoroTYLs 

B.  Herbaceous  Dicotyls 

C.  A\''oODY  Stemmed  Dicotyls 

vii 


06 
102 
107 


viii  CONTENTS 

PASS 

IV.     The  Work  of  Stems 112 

V.     Wood  Structure  in  its  Relation  to  Industrial  Uses      .  118 

VI.     Forestry 124 

Field  Work 128 

CHAPTER  V.  BUDS  AND  BRANCHES 

I.    Modes  of  Branching 131 

IT.     Buds 138 

III.     The  Branching  of  Flower  Stems 141 

Field  Work 145 

CHAPTER   VI.     THE   LEAF 

I.     The  Typical  Leaf  and  its  Parts 147 

II.     The  Veining  and  Lobing  of  Leaves 154 

III.  Transpiration 160 

IV.  Anatomy  of  the  Leaf 164 

V.     Food  Making 168 

VI.     The  Leaf  an  Organ  of  Respiration 174 

VII.     The  Adjustment  of  Leaves  to  External  Relations     .  177 

VIII.     Modified  Leaves 18t> 

Field  Work 194 


CHAPTER   VTL     THE    FLOWER 

I.  Dissection  of  Types  with  Superior  Ovary 

U.  Dissection  of  Types  with  Inferior  Ovary 

III.  Study  of  a  Composite  Flower 

IV.  Specialized  Flowei!s 
V.  Function  and  Work  of  the  Flower 

VI.     Hybridization 

VII.     Plant  Breeding        .... 
VIII.    Ecology  of  the  Flower 

A.  The  Prevention  of  Self-pollination 

B.  Wind  Pollixation 

C.  Insect  Pollination        .... 

D.  Protective  Adaptation 

flET.p  Work   ....-,, 


204 
210 
214 
210 
22;? 
230 

285 
239 
241 
245 
249 


CONTENTS  IX 
CHAPTER  VIII.    FRUITS 

PAGE 

I.    Horticultural  and  Botanical  Fruits       .        .                ,  250 

II.    Fleshy  Fruits .  255 

HI.     DuY  Fruits 260 

IV.     Accessory,  Aggregate,  and  Multiple  Fruits  .        .        .  265 

Field  Work 269 

CHAPTER  IX.     THE   RESPONSE  OF   THE   PLANT   TO 
ITS   SURROUNDINGS 

I.    Ecological  Factors 271 

II.     Plant  Associations 277 

III.  Zones  of  Vegetation 288 

Field  Work 294 

CHAPTER  X.     CRYPTOGAMS 

I.    TiiEiK  Place  in  Nature =        .  296 

II.     Alg^: 299 

HI.     Fungi 30=^ 

A.  Bacteria 306 

B.  Yeasts 314 

C.  Rusts 317 

D.  Mushrooms      ' 323 

IV.  Lichens       .                 329 

V.     Liverwortp 334 

VI.     INIossES 341 

VH.     Fern  Plants 344 

VIH.     The  Relation  between  Cryptogams  and  Seed  Plants  .  354 

IX.     The  Course  of  Plant  Evolution 359 

Field  Work 362 

APPENDIX 

1.  Systematic  Botany 364 

2.  Weights,  Measures,  and  Temperatures 367 


CHAPTER   I.     THE   SEED 
I.    THE    STORAGE    OF   FOOD   IN   SEEDS 

Material.  —  In  addition  to  the  four  food  tests  described  in  Exps. 
1-6,  there  should  be  provided  some  raw  starch,  a  solution  of  grape 
sugar,  the  white  of  a  hard-boiled  egg,  and  any  fatty  substance,  sucli 
as  lard  or  oil.  For  Exps.  8  and  9,  a  little  diastase  solution  will  be  nec- 
essary. "Taka"  diastase,  made  from  rice  acted  upon  by  a  fungus,  can 
be  obtained  for  a  trifle  at  almost  any  drug  store. 

Living  material.  —  Grains  of  corn  and  wheat,  and  seeds  of  some 
kind  of  bean,  the  larger  the  better.  The  "horse  bean"  (Vicia  faba),  if 
it  can  be  obtained,  makes  an  excellent  object  for  study,  as  the  cells  are 
so  large  that  they  can  be  seen  with  the  naked  eye.  For  showing  the 
presence  of  proteins  (aleurone  grains)  and  oily  matter,  use  thin  cross  sec- 
tions through  the  kernel  of  a  castor  bean  or  a  Brazil  nut.  Specimens 
for  the  study  of  the  individual  cell  will  be  found  in  the  hairs  growing  on 
squash  seedlings,  in  the  epidermis  of  one  of  the  inner  coats  of  an  onion,  in 
the  roots  of  oat  or  radish  seedlings,  or  in  the  section  of  a  young  corn  root. 

A  compound  microscope  will  be  required  for  this  study. 

I.  The  economic  importance  of  seeds.  —  As  a  source  of 
food  to  both  man  and  the  lower  animals,  the  importance  of 
seeds  can  hardly  be  overrated.  All  the  flour,  meal,  rice, 
hominy,  and  other  breadstuff s  sold  in  the  market  come  from 
them,  to  say  nothing  of  the  fleece  from  the  cotton  seed  that 
clothes  the  greater  part  of  the  world,  besides  furnishing  a 
substitute  for  lard  and  an  important  food  for  cattle.  The 
oils  and  fats  stored  in  nuts  are  also  to  be  taken  into  account, 
the  peanut  alone  yielding  the  greater  part  of  the  so-called 
olive  oil  of  commerce.  Since  the  value  of  our  farm  crops 
depends  largely  upon  the  kind  and  quantity  of  these  sub- 
stances furnished  by  them,  it  is  worth  our  while,  as  a  matter 
of  economic  as  well  as  scientific  interest,  to  learn  something 
about  the  nature  of  the  different  foods  contained  in  plants. 

nOfERU  LIBRARY 


PRACTICAL  COURSE  IN  BOTANY 


r\ 


1  2 

Figs.  1-3.  —  The  world's  three  most  important  food  grains  (magnified)  :  1,  sec- 
tion of  a  rice  grain  ;  a,  cuticle  ;  b,  aleurone,  or  protein  layer  ;  c,  starch  cells  ;  d,  germ  ; 
2,  section  of  a  wheat  grain  ;  k,  germ  ;  s,  starch  ;  a,  gluten  ;  t,  t,  t,  layers  of  the  seed 
coat ;  3,  section  of  a  grain  of  corn  ;  c,  husk  ;  e,  aleurone  layer  containing  proteins ; 
eg,  yellowish,  horny  endosperm,  containing  proteins  and  starch  ;  ew,  lighter  starchy 
endosperm  :  the  darker  part  below  is  rich  in  oil  and  proteins,  and  contains  the  eni' 
hryo,  consisting  of  the  absorbing  organ,  or  cotyledon,  sc;  the  rudimentary  bud,  s  ;  and 
the  root,  w.     (1,  from  Circular  77,  La.  Exp.  Station  ;  2,  from  France  ;  3,  from  Sachs.) 

2.  Why  food  is  stored  in  seeds.  —  The  one  purpose 
for  which  plants  produce  their  seed  is  to  give  rise  to  a  new 
generation  and  so  carry  on  the  life  of  the  species.  The 
seed  is  the  nursery,  so  to  speak,  in  which  the  germ  destined 

to  produce  a  new  plant 
is  sheltered  until  it  is 
ready  to  begin  an  inde- 
pendent existence.  But 
the  young  plant,  like 
the  young  animal,  is 
incapable  of  providing 
for  itself  at  first,  and 
would  die  unless  it  re- 
ceived nourishment  from 
the  mother  plant  until 

Figs.  4-7.  —  Sections  of  corn  grains  showing  -j.    v         r              i           j.           j 

different  qualities  of  food  contents :  4,  5,  small  ^^   '^^^  lOrmeQ  rOOtS  anQ 

germ  and  large  proportion  of  horny  part,  show-  leaVCS     SO     that     it     CaH 

ing  high  protein;  6, 7,  large  germ  and  smaller  pro-  c      -l              r       J      r 

portion  of  horny  part,  showing  high  oil  content,  manuiacture      lOOd     lOr 


THE  SEED 


itself.  Plants  in  general  require  very  much  the  same  food 
that  animals  do,  and  they  have  the  power,  which  animals 
have  not,  of  manufacturing  it  out  of  the  crude  materials  con- 
tained in  the  soil  water  and  in  the  air.  Such  of  these  foods 
as  are  not  needed  for  immediate  consumption,  they  store  up 
to  serve  as  a  provision  for  the  young  shoot  when  the  seed 
begins  to  germinate. 

3.  Food  substances  contained  in  seeds.  —  There  are  four 
principal  classes  of  food  stored  in  seeds:  sugars,  starches,  oils, 
and  proteins.  The  first  are  held  in  solution  and  can  be 
detected,  if  in  sufficient  quantity,  by  the  taste.  The  most 
important  varieties  of  this  group  are  cane  and  grape  sugar, 
the  latter  occurring  most  abundantly  in  fruits,  the  former  in 
roots  and  stems.  Oil  usually  occurs  in  the  form  of  globules. 
It  is  very  abundant  in  some  seeds,  e.g.  flax,  castor  bean,  and 
Brazil  nut.  In  the  corn  grain  it  is  found  in  the  part  constitut- 
ing the  germ,  or  embryo  (Figs.  6,  7).  Starches  and  proteins 
occur  in  the  form  of  small  granules,  which  have  specific 
shapes  in  different  plants  (Figs.  8,  9).  Those  containing  pro- 
teins are  called  aleurone  grains,  and  are,  as  a  rule,  smaller 
than  the  starch  grains  with  which  they  are  intermixed  in  the 
bean  and  some  other  seeds.  In  wheat,  corn,  rice,  and  most 
grains  they  form  a  layer  just  inside  the  husk,  as  shown  in 
Fig.  10.  This  is  the  reason  why  polished  rice  and  finely 
bolted  flour  are  less  nu- 
tritious than  the  darker 
kinds,  from  which  this 
valuable  food  substance 
has  not  been  removed. 
The  two  most  familiar 
kinds  of  proteins  are  the 
albumins,  of  which  the 
white  of  an  egg  is 
a  well-known  example, 

and  the  glutins,  which  give  to  the  dough  of  wheat  flour  and 
oatmeal  their  peculiar  gummy  or  "  glutinous  "  structure. 


Figs.  8-9.  —  Different  forms  of  starch  grains ; 
rice  ;  9,  wheat. 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  10. — Transverse  section  near  the 
outside  of  a  wheat  grain  :  e,  the  husk  ;  a,  cells 
containing  protein  granules  ;  s,  starch  cells 
{after  Tschirch). 


4.  Organic  foods.  —  These  four  substances,  starch,  sugar, 
fats,  and  proteins,  with  some  others  of  less  frequent  oc- 
currence, are  called  organic 
foods,  because  they  are  pro- 
duced, in  a  state  of  nature, 
only  through  the  action  of 
organized  living  bodies,  or, 
more  strictly  speaking,  of 
living  vegetable  bodies. 

5.  Our  dependence  upon 
plants. — ^  While  the  animal 
organism  can  digest  and 
assimilate  these  substances 
after  they  have  been  formed 
by  plants,  it  has  no  power 
to  manufacture  them  for 
itself,  and,  so  far  as  we  know  at  present,  is  wholly  depend- 
ent upon  the  vegetable  world  for  these  necessaries  of  life. 
In  one  sense  the  whole  animal  kingdom  may  be  said  to  be 
parasitic  on  plants.  The  wolf  that  eats  a  lamb  is  getting 
his  food  indirectly  from  the  grains  and  grasses  consumed 
by  its  victim,  and  the  lion  that  devours  the  wolf  that  ate 
the  lamb  is  only  one  step  further  removed  from  a  vegetable 
diet. 

6.  The  vegetable  cell.  —  If  you  will  break  open  a  well- 
soaked  horse  bean  and  examine  the  contents  with  a  lens,  you 
will  see  that  they  are  composed  of  small  oval  or  roundish 
granules  packed  together  like  stones  in  a  piece  of  masonry. 
These  little  bodies,  called  cells,  are  the  ultimate  units  out 
of  which  all  animal  and  vegetable  structures  are  built  up,  as 
a  wall  is  built  of  bricks  and  stones.  They  differ  very  much 
from  bricks  and  stones,  however,  in  that  they  are,  or  have 
been,  living  structures  with  their  periods  of  growth,  activity, 
decline,  and  death,  just  like  other  living  matter,  as  will  be 
seen  by  and  by,  when  we  come  to  look  more  particularly 
into  their  life  history.     They  consist  usually  of  an  inclos- 


THE  SEED  5 

ing  membrane  which  contains  a  living  substance  called 
protoplasm.  This  is  the  essential  part  of  the  cell,  and,  so 
far  as  we  know  at  present,  the  physical  basis  of  all  Hfe. 
Cells  are  commonly  more  or  less  rounded  in  shape,  though 
they  take  different  forms  according  to  the  purpose  they 
serve.  Sometimes,  as  in  the  fibers  of  cotton  and  the  down 
of  young  leaves,  they  are  long  and  hairlike ;  when  closely 
packed,  they  often  become  angular  by  pressure,  like  those 
shown  in  Figs.  10, 11.  The  cells  composing  the  thick  body  of 
the  bean  are  for  the  most  part  starch  and  other  substances 
stored  up  for  food,  which  render  observation  difficult.  It 
will,  therefore,  be  better  to  choose  for  a  study  of  the  indi- 
vidual cell  some  kind  that  will  show  the  essential  parts  more 
distinctly. 

7.  Microscopic  examination  of  a  cell.  —  Place  under  a  high 
power  of  the  microscope  a  portion  of  fresh  skin  from  one  of 
the  inside  scales  of  an  onion,  or  a  piece 
of  the  root  tip  of  a  very  young  corn  or  oat 
seedling,  and  fix  your  attention  on  one  of 
the  individual  cells.     Notice  (1)  the  cell  -w 

wall  or  inclosing  membrane,  w  (Fig.  11)  ;    ^ 

(2)  the  protoplasm,   p,  which  may  be 
recognized  by  its  granular  appearance ; 

(3)  thenwdeiis,  n;  and  (4)  thecellsap,  s.     "^i        ,   . 

In  very  young  cells  the  protoplasm  will  y^Sjl^  ^ 
be  seen  to  fill  most  of  the  interior;  but  p^^  11— Typical  cells: 
in  mature  ones,  like  the  large  one  on  the  «.  nucleus ;  p,  protoplasm ; 
right  of  the  figure,  it  forms  a  thin  lining  ^'  ^^  ^^ 
around  the  wall,  with  the  nucleus  on  one  side,  while  the  cell 
sap,  composed  of  various  substances  in  solution,  occupies  the 
central  portion.  Though  there  is  generally  an  inclosing  wall, 
this  is  not  essential,  its  office  being  to  give  strength  and  me- 
chanical support  by  holding  the  contents  together,  as  an 
India-rubber  bag  holds  water.  It  is  the  turgidity  of  the  cell, 
when  distended  with  liquid,  that  gives  firmness  to  herba- 
ceous plants  and  the  tender  parts  of  woody  ones.     This 


G  PRACTICAL  COURSE  IN  BOTANY 

may  be  illustrated  by  observing  the  difference  between  a 
rubber  bag  when  quite  full  and  when  only  half  full  of  water, 
or  a  football  when  partially  and  when  fully  inflated.  In 
its  simplest  form,  however,  the  cell  is  a  mere  particle  of 
protoplasm,  which  has  one  paj't,  constituting  the  nucleus, 
a  little  more  dense  in  appearance  than  the  rest,  but  this 
kind  is  not  common  in  vegetable  structures. 

8.  How  food  substances  get  into  the  cells.  —  As  there 
are  no  openings  in  the  cell  walls,  the  only  way  substances 
can  get  into  a  cell  or  out  of  it  is  by  soaking  through  the 
inclosing  membrane,  as  will  be  explained  in  a  later  chapter. 
Since  starch,  oil,  and  proteins,  the  most  important  foods 
stored  in  seeds,  are  none  of  them  soluble  in  the  cell  sap,  it  is 
clear  that  they  could  not  have  got  into  the  cells  in  their 
present  state,  but  must  have  undergone  some  change  by 
which  they  were  rendered  capable  of  passing  through  the 
cell  wall. 

9.  Digestion.  —  The  process  by  which  this  change  is 
brought  about  is  known  as  digestion,  from  its  similarity  to 
the  same  function  in  animals.  Not  only  are  foods,  in  the 
state  in  which  we  find  them  stored  in  the  seed,  incapable 
of  passing  through  the  cell  wall,  but  the  protoplasm,  the 
living  part  of  the  cell,  has  no  power  to  assimilate  and  to 
utilize  these  substances  as  food  until  they  have  been  re- 
duced to  a  soluble  form  in  which  they  can  be  diffused  freely 
from  cell  to  cell  through  any  part  of  the  plant.  By  diffusion 
is  meant  the  gradual  spread  of  soluble  substances  through 
the  containing  medium,  as  when  a  lump  of  sugar  or  salt, 
dropped  into  a  glass  of  water,  dissolves  and  slowly  diffuses 
through  the  contents,  imparting  a  sweet  or  salty  taste  to  the 
whole. 

During  the  process  of  digestion  the  different  kinds  of 
food  are  acted  upon  and  made  soluble  by  certain  chemical 
ferments,  which  are  secreted  in  plants  for  the  purpose.  The 
digestion  of  starch,  the  most  abundant  of  plant  foods,  is 
effected  by  diastase,  a  common  ferment  obtained  from  ger- 


THE  SEED 


^#®  J 


minating  grains  of  barley,  wheat,  corn,  rice,  etc.  By  the 
presence  of  diastase  starch  is  converted  into  grape  sugar,  a 
substance  which  is  readily  soluble  in  water,  and  which  can 
be  diffused  easily  through  the  tissues  of  the  plant  to  any 
part  where  it  is  needed.  In  this  way  food  travels  from  the 
leaf,  where  it  is  made,  to 
the  seed,  where  the  sugar  is 
generally  reconverted  into 
starch  and  stored  up  for 
future  use,  though  some- 
times, as  in  the  sugar  corn 
and  sugar  pea,  it  remains 
in  part  unchanged.  The 
kernels  of  this  kind  of  corn 
can  be  distinguished  readily 
from  those  of  the  ordinary 
starch  corn,  after  maturity, 
by  their  wrinkled  appear- 
ance, owing  to  their  greater 
loss  of  water  in  drying. 

ID.  Food  tests.  —  In  or- 
der to  tell  whether  any  of 
the  food  substances  named 
occur  in  the  seeds  that  we  are  going  to  examine,  it  will  be 
necessary  to  understand  a  few  simple  tests  by  which  their 
presence  may  be  recognized.  The  chemicals  required  can 
be  ordered  ready  for  use  from  a  druggist  or  may  be  prepared 
in  the  laboratory  as  needed,  according  to  the  directions 
given.  Write  in  your  notebook  a  brief  account  of  each  ex- 
periment made,  with  the  conclusions  drawn  from  it. 

Experiment  1 .  To  detect  the  presence  of  fats.  —  Rub  a  small  lump 
of  butter  or  a  drop  of  oil  on  a  piece  of  thin  white  paper.    What  is  the  effect  ? 

Experiment  2.  Another  test  for  fats.  —  Place  some  macerated 
alcanna  root  in  a  vessel  with  alcohol  enough  to  cover  it,  and  leave  for  an 
hour.  Add  an  equal  hulk  of  water  and  filter.  The  solution  will  stain 
fats,  oils,  and  resins  deep  red. 


Fig.  12.  —  Starch  grains  of  wheat  in 
different  stages  of  disintegration  under  the 
action  of  a  ferment  (diastase),  accompany- 
ing germination  :  a,  slightly  corroded  ;  h,  c, 
and  d,  more  advanced  stages  of  decomposi- 
tion. 


PRACTICAL  COURSE  IN  BOTANY 


THE  SEED  9 

Experiment  3.  To  show  the  presence  of  starch.  —  Put  a  drop  of 
iodine  solution  on  some  starch.  What  change  of  color  takes  place  ?  To 
make  iodine  solution,  add  to  one  part  of  iodine  crystals  4  parts  potas- 
sium iodide  and  95  parts  water.  It  should  be  kept  in  the  dark,  as  light 
decomposes  it.  Iodine  colors  starch  blue,  protein  substances  light  brown. 
In  testing  for  starch,  the  solution  should  be  diluted  till  it  is  of  a  pale  color, 
otherwise  the  stain  will  be  so  deep  as  to  appear  black. 

Experiment  4.  A  test  for  proteins.  —  Place  a  small  quantity  of 
the  white  of  an  egg,  diluted  with  water,  in  a  clean  glass  and  add  a  few 
drops  of  nitric  acid ;  or  drop  some  of  the  acid  on  the  white  of  a  hard- 
boiled  egg.     What  is  the  effect  ? 

Nitric  acid  turns  proteins  yellow ;  if  the  color  is  indistinct,  add  a  drop 
of  ammonia,  when  an  orange  color  will  ensue. 

Experiment  5.  Another  test  for  proteins.  —  Place  on  the  sub- 
stance to  be  examined  a  drop  of  a  saturated  solution  of  cane  sugar  and 
water ;  add  a  drop  of  pure  sulphuric  acid ;  if  proteins  are  present,  they 
will  be  colored  red.     See  also  Exp.  3. 

Experiment  6.  A  test  for  grape  sugar.  —  Heat  a  teaspoonful  of 
Fehling's  Solution  to  the  boiling  point  in  a  test  tube  (a  common  glass  vial 
can  be  used  by  heating  gradually  in  water)  and  pour  in  a  few  drops  of 
grape  sugar  solution.  Heat  again  and  observe  the  color  of  the  precipitate 
that  forms. 

Fehling's  Solution  may  be  obtained  of  the  druggist,  or,  if  preferred, 
it  may  be  prepared  in  the  laboratory  as  follows :  (a)  Dissolve  173  grams 
of  crystallized  Rochelle  salts  and  125  grams  of  caustic  potash  in  500  cc.  of 
water;  (6)  dissolve  34.64  grams  crystallized  copper  sulphate  in  500  cc. 
of  water,  and  mix  equal  parts  as  needed.  (For  English  equivalents,  see 
Appendix,  Weights  and  Measures.)  The  two  mixtures  must  be  kept  sep- 
arate till  wanted  for  use,  or  prepared  fresh  as  needed. 

Grape  Sugar  causes  Fehling's  Solution  to  form  a  red  precipitate. 

Experiment  7.  To  show  the  difference  between  sugar  and 
STARCH  IN  regard  TO  SOLUBILITY.  —  Mix  some  sugar  with  water  and 
notice  how  readily  it  dissolves.  Try  the  same  experiment  with  starch 
and  observe  its  different  behavior. 

Experiment  8.  To  show  how  starch  is  disintegrated  in  the  A'^t 
OF  DIGESTION.  —  Place  a  few  grains  of  starch  on  a  slide,  add  a  drop  or 
two  of  diastase  solution,  and  observe  under  the  microscope ;  the  starch 
granules  will  be  seen  to  disintegrate  and  melt  away.  Even  with  a  hand 
lens  it  can  be  seen,  from  the  greater  clearness  of  the  liquid  in  comparison 
with  a  mixture  of  untreated  starch  and  water,  that  the  gi-ains  have  been 
dissolved. 


10  PRACTICAL  COURSE  IN  BOTANY 

Experiment  9.  To  show  that  diastase  converts  starch  into 
SUGAR.  —  Make  a  paste  of  boiled  starch  so  thin  that  it  looks  like  water. 
Pour  a  small  quantity  of  it  into  each  of  two  tubes,  adding  a  little  diastase 
to  one  and  leaving  the  other  untreated.  Keep  in  a  warm  place  for  twenty- 
four  hours,  then  test  both  tubes  for  starch,  as  directed  in  Exp.  3,  and  note 
the  result.    If  the  diastase  has  not  acted,  add  a  little  more  and  watch. 

Practical  Questions 

1.  Name  all  the  food  and  other  economic  products  you  can  think  of 
that  are  derived  from  the  seed  of  maize;  from  wheat;  from  flaxseed; 
from  cotton. 

2.  Mention  some  seeds  from  which  medicines  are  procured. 

3.  Name  all  the  seeds  you  can  think  of  from  which  oil  is  obtained ; 
starch;    some  that  are  rich  in  proteins.     (Exps.  1-5.) 

4.  Describe  some  of  the  ways  in  which  these  products  are  frequently 
adulterated. 

5.  If  you  were  raising  corn  to  sell  to  a  starch  factory,  what  part  of 
the  seed  would  you  seek  to  develop  ?  If  to  feed  stock,  what  part  ?  Why, 
in  each  case?     (3;     Figs.  4-7.) 

6.  What  grain  feeds  more  human  beings  than  does  any  other  ? 

7.  Name  all  the  seeds  you  can  think  of  that  contain  sugar  in  sufficient 
quantity  to  be  detected  without  chemical  tests ;  that  is,  by  tasting  alone. 

8.  Is  "coal  oil"  a  mineral  or  an  organic  substance?  Explain,  by 
giving  an  account  of  its  origin. 

9.  What  is  gluten  ?  (3.)  Name  some  grains  that  are  especially  rich  in  it. 
10.  Which  of  our  three  chief  food  grains  is  a  water  plant  ?    (See  Plate 

2.)     Which  grows  farthest  south  ?    Which  farthest  north  ?    Which  one  is 
of  American  origin  ? 

n.    SOME  PHYSIOLOGICAL  PROPERTIES   OF   SEEDS 

Material. — Seeds  of  squash,  pumpkin,  or  other  melon;  castor  bean  ; 
any  kind  of  common  kidney  bean ;  grains  of  Indian  corn. 

Appliances.  —  In  the  absence  of  gas,  an  alcohol  or  kerosene  lamp  may 
be  used  for  heating.  A  double  boiler  can  easily  be  made  by  using  two  tin 
vessels  of  different  sizes.  Partly  fill  the  larger  one  with  water,  set  in  it 
the  smaller  one  with  the  substance  to  be  heated,  and  place  over  a  burner. 
A  pair  of  scales,  a  strong  six-ounce  bottle,  wire-netting,  cord,  and  wax 
or  paraffin  should  be  provided. 

Experiment  10.  Do  seeds  in  their  ordinary  quiescent  state 
CONTAIN  ANY  WATER?  —  Placc  a  number  of  beans,  or  grains  of  corn  or 
wheat  in  a  glass  bottle,  making  a  small  perforation  in  the  cork  to  allow 
the  air  to  escape,  and  heat  gently.     Does  any  moisture  form  on  the  glass  ? 


THE  SEED 


11 


A  better  test  is  to  weigh  two  or  three  ounces  of  seeds,  and  heat  them 
in  a  double  boiler  or  in  oil  to  prevent  scorching.  Weigh  at  intervals.  If 
ihcre  is  any  loss  of  weight,  to  what  is  it  due? 

l']xPERiMENT  11.  Do  SEEDS  ABSORB  WATER?  —  Soak  a  number  of 
hr-ans  or  grains  of  coi-n  in  water  for  12  to  24  hours  and  compare  with 
dry  ones.     What  difference  do  you  notice  ?     To  what  cause  is  it  due  ? 

I'].\PERIMENT  12.       lluVV    UID   WATER  GET   INTO  THE  SOAKED  SEEDS?  — 

Dry  gently  with  a  soft  cloth  some  of  the  seeds  used  in  the  last  experiment 
and  press  them  lightly  to  see  if  water  comes  out,  and  where.  Place  a  num- 
ber of  dry  seeds  of  different  kinds  —  squash,  bean,  castor  bean,  quince, 
etc.  —  in  warm  water  and  notice  whether  any  bubbles  of  air  form  on  them 
and  at  what  point.  Examine  with  a  lens  and  see  if  this  point  differs  in  any 
way  from  the  rest  of  the  seed  cover.  Does  it  correspond  with  the  point 
from  which  water  exuded  in  the  soaked  seeds?  Could  hard  seeds  like 
the  squash,  castor  bean,  buckeye,  and  Brazil  nut  get  water  readily  without 
an  opening  somewhere  in  the  coat  ? 

EXPERIMBNT    13.        To     FIND     OUT     WHETHER     WATER     IS     ABSORBED 

THROUGH  THE  SEED  COATS. — Placc  in  moist  sand  or  sawdust  two  rows 
of  beans  as  nearly  as  possible  of  the  same  size  and  weight,  with  the  eye 
pressed  down  to  the  substratum  in  one  row  and  turned  up  in  the  other,  so 
that  no  moisture  can  enter  through  it.  In  the  same  way  arrange  two 
rows  of  castor  beans  with  the  little  end  down  in  one  row  and  uppermost 
in  the  other.  In  the  last  set  carefully  break  away  the  spongy  mass  near 
the  tip,  without  injuring  the  parts  about  it.  Watch  and  see  in  which 
rows  water  is  absorbed  most  readily.  What  change  takes  place  in  the 
spongy  masses  at  the  tips  of  those  castor  beans  on 
which  they  were  left  ? 

Experiment  14.     Is 


THE  rate  of  germina- 


tion AFFECTED  BY  THE  PRESENCE  OR  ABSENCE  OF 

openings  ?  —  Seal  up  with  wax  or  paraffin  all  the 
openings  of  a  number  of  air-dry  peas  or  beans,  and 
leave  an  equal  number  of  the  same  size  and  weight 
untreated.  Be  careful  that  the  sealing  is  absolutely 
water-tight,  since  otherwise  the  experiment  will 
be  worthless.  Plant  both  sets  and  keep  under  like 
conditions  of  soil,  temperature,  and  moisture.  Do 
you  see  any  difference  in  the  rate  of  germination  of 
the  two  sets? 

Experiment  15.  Do  seeds  exert  force  in 
/*  BSORBiNG  WATER  ?  —  Fill  a  commou  six-ounce  bot- 
tle as  full  as  it  will  hold  with  dry  peas,  beans,  or 


Fig.  13.  —  Effect 
of  the  expansion  of 
seeds  due  to  absorp- 
tion of  water. 


12  PRACTICAL  COURSE   IN  BOTANY 

grains  of  com;  then  pour  in  water  till  the  bottle  is  full.  Tie  a  piece  of 
wire-netting  or  stout  sackcloth  over  the  top  to  keep  the  seeds  from  being 
forced  out.  Bind  both  the  neck  and  the  body  of  the  Ijottle  tightly  with 
strong  cords  encircling  it  in  both  a  horizontal  and  vertical  direction,  and 
place  under  water  in  a  moderately  warm  temperature.  Watch  for  results. 
Experiment  16.  Is  the  force  exerted  in  the  last  experiment 
A  merely  mechanical  one,  like  the  bursting  of  a  water  pipe,  or 

IS    IT    PHYSIOLOGICAL    AND    THUS    DEPENDENT    ON    THE    FACT   THAT   THE 

SEEDS  ARE  ALIVE  ?  —  To  auswcr  this  question  try  Exp.  15  with  seeds 
that  have  been  killed  by  heat  or  by  soaking  in  formalin. 

Practical  Questions 

1.  Will  a  pound  of  pop  corn  weigh  as  much  after  being  popped  as  be- 
fore?    (Exp.  10.) 

2.  What  causes  the  difference,  if  there  is  any?     (Exp.  10.) 

3.  Does  the  tuft  of  downy  hairs  at  the  tip  of  wheat  and  oat  grains 
influence  their  water  supply  ?  The  spongy  covering  of  black  walnuts  and 
almonds?  The  pithy  inside  layers  of  pecans  and  English  walnuts? 
(Exps.  12,  13.) 

4.  Why  will  seeds,  as  a  general  thing,  germinate  more  readily  after 
being  soaked?     (Exps.  11,  14,  16.) 

III.   TYPES    OF   SEEDS 

Material.  —  Dry  and  soaked  grains  of  corn,  wheat,  or  oats ;  bean, 
squash,  castor  bean,  and  pine  seed,  or  any  equivalent  specimens  showing 
the  differences  as  to  number  of  cotyledons  and  the  presence  or  absence  of 
endosperm.  Each  student  should  be  provided  with  several  specimens, 
both  soaked  and  dry,  of  the  kind  under  consideration.  Corn,  beans,  and 
wheat  need  to  be  soaked  from  12  to  24  hours ;  squash  and  pumpkin  from 
2  to  5  days,  and  very  hard  seeds,  like  the  castor  bean  and  morning-glory, 
from  5  to  10.  If  such  seeds  are  clipped,  before  soaking,  that  is,  if  a  small 
piece  of  the  coat  is  chipped  away  from  the  end  opposite  the  scar,  or  eye, 
they  will  soften  more  quickly.  Keep  them  in  a  warm  place  with  an  even 
temperature  till  just  before  they  begin  to  sprout,  when  the  contents  become 
softened.  Very  brittle  cotyledons  may  be  softened  quickly  by  boiling 
for  a  few  minutes. 

No  appliances  are  needed  beyond  the  pupil's  individual  outfit  and  some 
of  the  food  tests  given  in  Section  I  of  this  chapter. 

II.  Dissection  of  a  grain  of  corn.  —  Examine  a  dry  grain 
of  corn  on  both  faces.  Wliat  differences  do  yon  notice? 
Sketch  the  grooved  side,  labeUng  the  hard,  yellowish  outer 


THE   SEED 


13 


portion,  endosperm,  the  depression  near  the  center,  embryo,  or 
germ. 

Next  take  a  grain  that  has  been  soaked  for  twenty-four 
hours.  \Vhat  changes  do  you  see  ?  How  do  you  account  for 
the  swelling  of  the  embryo?  Remove  the  skin  and  observe 
its  texture.  Make  an  enlarged  sketch  of  a  grain  on  the 
grooved  side  with  the  coat  removed,  labeling  the  fiat  oval  body 
embedded  in  the  endosperm,  cotyledon ;  the  upper  end  of  the 
little  budlike  body  embedded  in  the  cotyledon,  plumule,  the 
lower  part,  hypocotyl— words 
meaning,  respectively, "  seed 
leaf,"  "little  bud,"  and 
"  the  part  under  the  cotyle- 
don." As  this  part  has  not 
yet  differentiated  into  root 
and  stem,  we  cannot  call  it 
by  either  of  these  names. 
The  cotyledon,  hypocotyl, 
and  plumule  together  com- 
pose the  embryo.  Pick  out 
the  embryo  and  sketch  as 
it  appears  under  the  lens. 
Crush  it  on  a  piece  of  white  paper;  what  does  it  contain? 

Make  a  vertical  section  of  another  soaked  grain  at  right 
angles  to  its  broader  face,  and  sketch,  labeling  the  parts  as 
they  appear  in  profile.  Make  a  cross  section  through  the 
middle  of  another  grain  and  sketch,  labeling  the  parts  as  be- 
fore. What  proportion  of  the  grain  is  endosperm  and  what 
embryo  ?  Put  a  drop  of  iodine  and  of  nitric  acid  separately 
on  pieces  of  the  endosperm,  and  note  the  effects.  Test  the 
seed  coats  and  the  cotyledon  to  see  if  they  contain  any  starch. 

Notice  that  the  corn  grain  has  but  one  cotyledon,  hence 
such  seeds  are  said  to  be  monocotyledonous,  or  one-cotyledoned. 
The  grains  are  not  typical  seeds,  but  are  selected  for  examina- 
tion because  they  are  large  and  easy  to  handle,  can  be  ob- 
tained everywhere,  and  germinate  readily. 


14  15  10 

Figs.  14-16.  —  Dissection  of  a  grain  of 
corn  :  14,  soaked  grain,  seen  flatwise,  cut 
away  a  little  and  slightly  enlarged,  so  as  to 
show  the  embryo  lying  in  the  endosperm  ; 
15,  in  profile  section,  dividing  the  grain 
through  the  embryo  and  cotyledon  ;  16,  the 
embryo  taken  out  whole.  The  thick  mass  is 
the  cotyledon  ;  the  narrow  body  projecting 
upwards,  the  plumule  ;  the  short  proje?  ion 
at  the  base,  the  hypocotyl  {after  Gray). 


14 


PRACTICAL  COURSE  IN  BOTANY 


17  18 

Figs.  17,  18.  — A  kid- 
ney bean  :  17,  side  view  : 
18,  front  \new,  showing  /j, 
liilum,  m,  micropyle. 


12.  Dissection  of  a  bean.  —  Sketch  a  dry  bean  as  it  lies  in 
the  pod,  showing  its  point  of  attachment  and  any  markings 
that  may  appear  on  its  surface.  Then  take  it  from  the  pod  and 
examine  the  narrow  edge  by  which  it  was  attached.  Notice 
the  rather  large  scar  (commonly  called  the  eye  of  the  bean) 
where  it  broke  away  from  the  point  of 
attachment.  This  is  the  hilum.  Near  the 
hilum,  look  for  a  minute  round  pore  hke 
a  pinhole.  This  is  called  the  micropyle, 
from  a  Greek  word  meaning  "  a  little 
gate,"  because  it  is  the  entrance  to  the 
interior  of  the  seed  coat.  There  was  no 
micropyle  observed  in  the  corn  grain, 
because  it  is  not  a  true  seed  but  a  fruit 
inclosing  a  single  seed.  The  inclosing 
membrane  is  the  fruit  skin,  w^hich  has  become  incorporated 
wdth  the  seed  coat  and  taken  its  place  as  a  protective  covering. 
Compare  a  soaked  bean  with  a  dry  one ;  what  difference  do 
you  perceive  ?  How  do  you  account  for  the  change  in  size  and 
hardness?  Find  the  hilum  and  the  micropyle  in  the  soaked 
bean.  Lay  it  on  one  side  and  sketch,  with  the  micropyle  on 
top  ;  then  turn  toward  you  the  narrow  edge  that 
was  attached  to  the  pod  and  sketch,  labeling  all 
the  parts.  ]\Iake  a  section  through  the  long  diam- 
eter at  right  angles  to  the  flat  sides,  press  it 
slightly  open,  and  sketch  it.  Notice  the  line  or 
slit  that  seems  to  cut  the  section  in  half  longitu- 
dinally, and  the  small  round  object  between  the 
halves  at  one  end  ;  can  you  tell  what  it  is  ? 

Slip  off  the  coat  from  a  whole  bean  and  notice  its 
texture.  Hold  it  up  to  the  light  and  see  if  it  shows 
any  signs  of  veining.  See  whether  the  scar  at  the  hilum  extends 
through  the  kernel,  or  marks  only  the  seed  coat.  Lay  open  the 
two  flat  bodies  into  which  the  kernel  divides  when  stripped  of 
its  coats,  keeping  them  side  by  side,  with  the  part  above  the 
micropyle  toward  the  top.     Sketch  their  inner  face  and  label 


THE  SEED  15 

them  cotyledons.  Be  careful  not  to  break  or  displace  the  tiny- 
bud  packed  away  between  the  cotyledons,  just  above  the 
hilum.  Label  the  round  portion  of  this  bud,  hypocotyl,  and 
the  upper,  more  expanded  part,  plumule.  Which  way  does  the 
base  of  the  hypocotyl  point ;  toward  the  micropyle,  or  away 
from  it  ?  Pick  out  this  budlike  body  entire  and  sketch  as  it  ap- 
pears under  the  lens.  Open  the  plumule  with  a  pin  and  exam- 
ine it  with  a  lens  ;  of  what  does  it  appear  to  consist  ?  Do  you 
find  any  endosperm  around  the  cotyledons,  as  in  the  corn  and 
oats  ?  Break  one  of  the  soaked  cotyledons,  apply  the  proper 
tests  (Exps.  2,  3,  5),  and  report  what  substances  it  contains. 
Wliere  is  the  nourishment  for  the  young  plant  stored  ?  What 
part  of  the  bean  gives  it  its  value  as  food  ? 

Notice  that  in  the  bean  the  embryo  consists  of  three  parts, 
the  hypocotyl,  plumule,  and  the  two  cotyledons,  which  com- 
pletely fill  the  seed  coats,  leaving  no  place  for  endosperm. 
Seeds  like  the  bean,  squash,  and  castor  bean,  which  have 
two  cotyledons,  are  said  to  be  dicotyledonous. 

13.  The  castor  bean.  —  Lay  a  castor  bean  on  a  sheet 
of  paper  before  you  with  its  fiat  side  down;  what  does  it 
look  like?  The  resemblance  may  be  increased  by  soaking 
the  seed  a  few  minutes,  in  order  to  swell  the  two  little  pro- 
tuberances at  the  small  end.  Can  you  think  of  any  benefit 
a  plant  might  derive  from  this  curious  resemblance  of  its  seed 
to  an  insect? 

Sketch  the  seed  as  it  lies  before  you,  labeling  the  pro- 
tuberance at  the  apex,  caruncle.  The  caruncle  is  an  append- 
age of  the  seed-covering  developed  by  various  plants;  its  use 
is  not  always  clear.  What  appears  to  be  its  object  in  the 
castor  bean?  Refer  to  Exp.  13  and  see  if  there  is  any  other 
purpose  it  might  serve. 

Turn  the  seed  over  and  sketch  the  other  side.  Notice  the 
colored  line  or  stripe  that  runs  from  the  large  end  to  the  car- 
uncle. This  is  the  rhaphe,  and  shows  the  position  that 
would  be  occupied  by  the  seed  stalk  if  it  were  present.  Its 
starting  point  near  the  large  end,  which  is  marked  in  fresh 


16 


PRACTICAL  COURSE  IN  BOTANY 


seeds  by  a  slight  roughness,  is  the  chalaza,  or  organic  base  of 
the  seed,  where  the  parts  all  come  together  like  the  parts  of  a 
flower  at  their  insertion  on  the  stem.  Where  was  it  situated 
in  the  common  bean?  How  does  this  differ  from  its 
position  in  the  castor  bean  ?  Where  the  rhaphe  ends, 
just  at  the  beak  of  the  caruncle,  you  will  find  the  hilum. 
The  micropyle  is  covered  by  the  caruncle,  which  is  an 
outgrowth  around  it. 

Now  cut  a  vertical  section  through  a  seed  that  has  been 
soaked  for  several  days,  at  right  angles  to  the  broad  sides, 
and  sketch  it.  Label  the  white,  pasty  mass  within  the 
seed  coats,  endosperm.  Can  you  make  out  what  the  narrow 
white  line  running  through  the  center  of  the  endosperm,  divid- 
ing it  into  two  halves,  represents?     Make  a  similar  sketch 

of  a  cross  section. 
Notice  the  same 
white  line  running 
horizontally  across 
the  endosperm,  di- 
viding it  into  two 
equal  parts.  To 
find  out  what  these 
lines  are,  take  an- 
other seed  (always 
use  soaked  seeds  for 
dissection)  and  remove  the  coats  without  injuring  the  kernel. 
Split  the  kernel  carefully  round  the  edges,  remove  half  the 
endosperm ,  and  sketch  the  other  half  with  the  delicate  em- 
bryo lying  on  its  inner  face.  You  will  have  no  difficulty 
now  in  recognizing  the  linos  in  your  drawings  as  sections  of 
the  thin  cotyledons.  Where  is  the  hypocotyl,  and  which  way 
does  its  base  point  ?  Remove  the  embryo  from  the  endosperm, 
separate  the  cotyledons  with  a  pin,  hold  them  up  to  the  light, 
and  observe  their  beautiful  texture.  Sketch  them  under  the 
lens,  showing  the  delicate  venation.  Is  there  any  plumule  ? 
Test  the  endosperm  with  a  little  iodine.    Does  it  give  a 


Figs.  20-22.— Castor  bean  (slightly  magnified)  ;  20, 
back  \'iew  ;  21,  front  view  ;  ch,  chalaza  ;  r,  rhaphe  ;  ca, 
caruncle  ;  22,  vertical  section  ;en,  endosperm  ;  cc,  cotyle- 
dons ;  hy,  hypocotyl ;  hi,  hilum  ;  m,  micropyle. 


THE  SEED 


17 


blue  or  a  brown  reaction  ?  Crush  another  bit  of  it  on  a  piece 
of  white  paper  and  see  if  it  leaves  a  grease  spot.  What  does 
this  show  that  it  contains  ?  Test  the  embryo  in  the  same  way, 
and  see  whether  it  contains  any  oil. 

Note.  —  It  should  be  borne  in  mind  that  the  castor  bean  bears  no  rela- 
tion whatever  to  the  true  beans.  It  belongs  to  the  sp\n-ge  family,  whi(^h 
is  botanically  very  remote  from  that  of  the  peas  and  beans. 


h.-- 

23  24  25 

Figs.  23-25. — Seed  of  a  squash;  23,  seed  from  the  outside;  24,  vertical  section 
perpendicular  to  the  broad  side  ;  25,  section  parallel  to  the  broad  side,  showing  inner 
side  of  a  cotyledon  ;  a,  seed  coat ;  c,  cotyledons  ;  /;,  hypocotyl ;  p,  plumule. 

14.  Study  of  a  squash  or  gourd  seed.  —  How  does  the  coat 
of  a  squash  seed  differ  from  that  of  the  bean  ?  At  the  small 
end,  look  for  two  dots,  or  pinholes,  close 
together.  Refer  to  your  drawing  of  the 
bean  and  see  if  you  can  make  out,  with 
the  help  of  a  lens,  what  they  are.  The 
bean  is  a  curved  seed,  which  is  bent  so  as 
to  bring  the  hilum  close  to  the  micropyle 
on  one  side.  But  by  far  the  greater 
number  of  seeds  are  inverted,  or  turned 
over  on  their  stalks,  as  you  sometimes 
see  huckleberry  blossoms  and  bell  flowers 
on  their  stems,  so  that  when  the  stalk 
breaks  away  from  its  attachment,  the 
scar  and  the  micropyle  come  close  to- 
gether at  one  end,  as  in  the  squash  seed. 

Make  a  drawing  of  the  outside  of  a 
seed,  labeling  all  the  parts  you  have  observed;  then  gently 


Fig.  26.  —  Diagram  of 
an  inverted  or  anatro- 
pous  seed,  showing  the 
parts  in  section  :  o,  outer 
coat ;  h,  inner  coat ;  c, 
kernel;  d,  rhaphe ;  ch, 
chalaza;  ft.  hilum;  m, 
micropyle  (After  Gray). 


18  PRACTICAL  COURSE   IN  BOTANY 

remove  the  hard  coat,  or  testa,  as  it  is  called.  The  thin,  green- 
ish covering  that  lines  it  on  the  inside  is  the  endosperm.  How 
does  it  compare  in  quantity  with  that  in  the  corn  anil  castor 
bean?  How  do  the  cotyledons  compare  in  thickness  with 
those  of  the  bean  ?  ( 'aref  ully  separate  them  and  draw,  label- 
ing the  parts  as  you  make  them  out.  The  tiny  pointed 
object  between  the  cotyledons  at  their  point  of  union  is  the 
plumule ;  is  it  as  well  developed  as  in  the  bean  ?  Can  you  see 
any  reason  why  seeds  like  the  pea  and  bean,  which  have  coty- 
ledons too  thick  and  clumsy  to  do  well  the  work  of  true  leaves, 
should  have  a  well-developed  plumule,  while  those  with  thin 
cotyledons,  like  the  squash  and  pumpkin,  do  not,  as  a  general 
thing,  form  a  large  plumule  in  the  embryo  ?  The  little  pro- 
jection in  which  the  cotyledons  end  is  the  hypocotyl;  which 
way  does  it  point  ?  Where  did  you  find  the  micropyle  to  be  ? 
Test  the  cotyledons  and  some  of  the  endosperm  for  food  sub- 
stances ;  what  do  you  find  in  them  ? 

15.  Study  of  a  pine  seed.  —  Remove  one  of  the  scales  from 
a  pine  cone  and  sketch  the  seed  as  it  lies  in  place  on  the  cone 
scale.  Notice  its  point  of  attachment  to 
the  scale,  and  look  near  this  point  for  a 
small  opening,  which  you  can  easily  recog- 
nize as  the  micropyle.  The  seed  with  its 
wing  looks  very  much  like  a  fruit  of  the 
maple,  but  differs  from  it  in  being  a  naked 
27         28.       seed  borne  on  the  inner  side  of  a  cone  scale. 

Figs.   27,    28.  —  .  ,  ,  1        ,  •  p 

Pitch  pine  seeds:  without  a  pod  or  husk  or  outer  covermg  of 
27,   scale,  or  open    ^j^y  ^i^d,  such  as  bcans  and  nuts  and  grains 

carpel,  with  one  seed  *^  •  i     i         ■  i  ^•^  1  • 

in  place ;  28  winged     are  provided  With.      Plants  like  the  pine, 

seed,  removed.  Ufter      ^^^^^^  ^^^^  ^j^^-^.  ^^^^   •  ^^  ^j^-^  ^.^^^  ^^^  ^^ij^^ 

Gymnosperms,  a  word  that  means  "  naked 
seeds,"  in  contradistinction  to  the  Angiosperms,  which  bear 
their  seeds  in  pods  or  other  closed  envelopes. 

Remove  the  coat  from  a  seed  that  has  been  soaked  for 
twenty-four  hours,  and  examine  it  with  a  lens.  Does  it  con- 
sist of  one  or  more  layers?    Is  there  any  difference  in  color 


THE   SEED 


19 


between  the  inner  and  outer  layers  ?  Look  at  the  base  of  the 
hypocotyl  for  some  loose,  cobwebby  appendages.  These  are 
the  remains  of  other  embryos  with  certain  append- 
ages belonging  to  them  that  were  formed  in  the 
endosperm,  but  failed  to  develop.  Did  you  find 
remains  of  this  kind  in  any  of  the  other  seeds  ex- 
amined? Pick  out  the  embryo  from  the  endo- 
sperm and  test  both  for  food  substances.  Which 
of  these  do  you  find  ?  Which  are  absent  ?  How 
does  the  embryo  differ  from  those  already  exam- 
ined ?  How  many  cotyledons  are  there  ?  Make 
an  enlarged  sketch  of  a  seed  in  longitudinal 
section,  labeling  correctly  all  the  parts  observed. 

i6.  Comparison  as  to  food  value  of  seeds.  —  Make  in  your 
notebook  a  tabular  statement  after  the  model  here  given,  of 
the  food  contents  found  in  the  different  seeds  you  have  ex- 
amined. Indicate  the  relative  quantity  of  each  by  writing 
under  it,  in  the  appropriate  column,  the  words,  "  much," 
"  little,"  or  "  none,"  as  the  case  may  be. 

By  far  the  greater  number  of  seeds  contain  endosperm ; 
that  is,  they  consist  of  an  embryo  with  more  or  less  nourishing 


Model  for  Record  of  Seeds  Examined 

Foods  Tested 

Starch 

Sugar 

Oil 

Proteins 

Com     .... 

Wheat  .... 

Bean     .... 

Squash.     .     .     . 

Castor  bean  .     . 

Pine      .... 

20  PRACTICAL  COURSE  m  BOTANY 

matter  stored  about  it.  Even  in  seeds  which  appear  to 
have  none,  the  endosperm  is  present  at  some  period  during 
development,  but  is  absorbed  by  the  cotyledons  before  ger- 
mination, 

17.  Manner  of  storing  nourishment.  —  In  the  various  seeds 
examined,  we  have  seen  that  the  nourishment  for  the  young 
plant  is  either  stored  in  the  embryo  itself,  as  in  the  coty- 
ledons of  the  bean,  acorn,  squash,  etc.,  or  packed  about  them 
in  the  form  of  endosperm,  as  in  the  corn,  wheat,  and  castor 
bean. 

18.  The  nimiber  of  cotyledons.  —  Seeds  are  also  classed 
according  to  the  number  of  their  cotyledons,  as  having  one 
two,  or  many  cotyledons.  The  first  two  kinds  make  up  the 
great  class  of  Angiosperms,  which  includes  all  the  true  flower- 
ing plants  and  forms  the  most  important  part  of  the  vegeta- 
tion of  the  globe.  The  last  is  characteristic  of  the  great 
natural  division  of  Gymnosperms,  or  naked-seeded  plants, 
of  which  we  have  had  an  example  in  the  pine.  They  are  the 
most  primitive  type  of  living  seed-bearing  plants.  Though 
they  are  not  so  abundant  now  as  in  past  ages,  numbering 
only  about  four  hundred  known  species,  they  present  many 
diversities  of  form,  which  seem  to  ally  them  on  the  one  hand 
with  the  lower,  or  spore-bearing  plants  (ferns,  mosses,  etc.), 
and  on  the  other  hand  with  the  Angiosperms. 

Practical  Questions 

1.  Make  a  list  of  all  the  seeds  you  can  find  that  have  verj'^  thick  coty- 
ledons, and  underline  those  that  are  used  as  food  by  man  or  beast. 

2.  Make  a  similar  list  of  all  the  kinds  with  thin  cotyledons  and  more  or 
less  endosperm,  that  are  used  for  food  or  other  purposes. 

3.  Do  you  find  a  greater  number  of  foodstuffs  among  the  one  kind 
than  the  other  ? 

4.  How  do  the  two  kinds  compare,  as  a  general  thing,  in  size  and 
weight  ? 

5.  From  what  part  of  the  castor  bean  do  we  get  oil  ?  of  the  peanut  ? 
of  cotton  seed?     (Exps.  1-6.) 

6.  Is  there  any  valid  objection  to  the  wholesomeness  of  peanut  oil,  and 
of  cottonseed  lard  as  compared  with  hog's  lard  ?    (1,  3.) 


THE   SEED  21 

7.  What  is  bran?  Does  it  contain  any  nourishment?  (11, 12;  Exps.  1-0.) 

8.  What  gives  to  Indian  corn  its   value  as  food?   to  oats?    wlieat  ? 
rice?     (3;    Exps.  1-6.) 

9.  Which  of  these  grains  has  the  larger  proportion  of  endosperm  to 
embryo  ?     (Figs.  1-3.) 

10.  Which  contains  the  lai'ger  amount  of  starch  in  proportion  to 
its  bulk,  rice  or  Indian  corn  ? 

11.  If  you  wished  to  produce  a  variety  of  corn  rich  in  oil,  you  would 
select  seed  for  planting  with  what  part  well  developed?     (3;  Figs.  4-7.) 

IV.    SEED   DISPERSAL 

Material.  —  Fruits  and  seeds  of  any  kind  that  show  adaptations  for 
dispersal.  Some  common  examples  are:  (1)  Wind:  ash,  elm,  maple, 
ailanthus,  milkweed,  clematis,  sycamore,  linden,  dandelion,  thistle, 
hawkweed.  (2)  Water:  pecan,  filbert,  cranberry,  lotus,  hickory  nut, 
coconut  —  obtain  one  with  the  husk  on,  if  possible.  (3)  Animal  agency 
(involuntary):  cocklebur,  tickseed,  beggar-ticks,  burdock;  (voluntary) 
almost  all  kinds  of  edible  fruits,  especially  the  bright-colored  ones  —  wild 
plums,  cherries,  haws,  dogwood,  persimmons,  etc.  (4)  Explosive  and 
self-planting :  witch-hazel,  wood  sorrel,  violet,  crane's-bill,  wild  vetch, 
peanut,  medick,  stork's-bill  (Erodium). 

Experiment  17.  To  show  how  seeds  are  dispersed  by  wind.  — 
Take  a  number  of  winged  and  plumed  fruits  and  seeds,  such  as  those  of  the 
maple,  ash,  ailanthus,  dandelion,  clematis,  milkweed,  and  trumpet  creeper; 
stand  on  a  chair  or  table  in  a  place  where  there  is  a  draft  of  air  and  let 
them  all  go.  Which  travel  the  farther,  the  winged  or  the  plumed  kinds  ? 
Which  sort  is  better  fitted  to  aerial  transportation  ? 

Experiment  18.  Dispersal  by  water.  —  Place  in  a  bucket  of  water 
a  hazelnut,  an  acorn,  an  orange,  a  cranberry,  a  pecan,  a  hickory  nut,  a  fresh 
apple,  and  a  coconut  with  the  husk  on.  Which  are  the  best  floaters  ?  Cut 
open  or  break  open  the  good  swimmers,  compare  with  the  non-floaters,  and 
see  to  what  peculiarity  of  structure  their  floating  qualities  are  due.  In 
what  situations  do  the  cranberry  and  the  coconut  grow  ?  Can  you  see 
any  advantage  to  a  plant  so  situated  in  producing  fruits  that  float  easily  ? 

Experiment  19.  Dispersal  by  explosive  capsules.  —  Moisten 
slightly  some  mature  but  unopened  capsules  of  witch  hazel,  wood  sorrel, 
rabbit  pea,  or  violet,  and  leave  in  a  warm,  dry  place  for  fifteen  to  forty- 
five  minutes.  What  happens  when  the  pods  begin  to  dry  ?  Measure  the 
distance  to  which  the  difl'erent  kinds  of  seeds  have  been  ejected.  Which 
were  thrown  farthest?  What  was  the  object  of  the  movement?  What 
caused  the  explosion  ? 


22 


PRACTICAL  COURSE   IN  BOTANY 


Experiment  20.  The  use  of  adhesive  fruits.  —  Scatter  broadcast 
a  handful  of  hooked  or  prickly  seeds  or  fruits  —  cocklebur,  tickseed,  beggar- 
ticks,  bur  grass,  etc.  Are  they  suited  for  wind  transportation  ?  Drop  one 
of  them  on  your  sleeve,  or  on  the  coat  of  a  fellow  student ;  will  it  stay 
there?  What  would  be  the  effect  if  it  became  attached  to  the  fur  of  a 
roaming  animal  ?    Is  this  a  successful  mode  of  dissemination  ? 


30 

Figs.  30-32.  —  30,  A  pod  of  wild  vetch,  with  mature  valves  twisting  spirally  to 
discharge  the  seed  ;  31,  pod  of  crane's-bill  discharging  its  seed  ;  32,  capsules  of  witch- 
hazel  exploding. 

ig.  Agencies  of  dispersal.  —  The  means  at  nature's  dis- 
posal for  this  purpose,  as  show^n  by  the  experiments  just  made, 
are  four ;  namely,  wind,  water,  the  explosion  of  capsules  due 
to  the  withdrawal  of  water,  and  the  agency  of  animals,  in- 
cluding man.     The  first  three  are  purely  mechanical.     The 


34  35 

Figs.  33-3G.  ^ — Fruits  adapted  to  wind  dispersal :  33,  winged  pod  of  pennycress  ; 
34,  spikclet  of  broom  sedge  ;  35,  akene  of  Canada  thistle  ;  36,  head  of  rolling  spin- 
ifex  grass. 

last,  animal  agency,  is  either  voluntary  or  involuntary,  ac- 
cording as  it  is  conscious  and  intentional,  or  accidental  merely. 
Man,  of  course,  is  the  only  consciously  voluntary  agent.    Of 


THE  SEED 


23 


the  four  agencies  named,  animals  and  wind  are  the  most  effec- 
tive, and  the  greater  number  of  adaptations  observed  will  be 
found  to  have  reference  to  these. 

Involuntary  dispersal.  —  The  lower  animals  may  be 


20. 


voluntary  agents  in  a  way,  though  not  designedly  so,  as  when 


Fig.  37.— Good  quality  of  clo- 
ver seed. 


Fig.  38.  —  Inferior  quality  of 
clover  seed  mixed  with  "  screen- 
ings." 


a  squhrel  buries  nuts  for  his  own  use  and  then  forgets  the  lo- 
cation of  his  hoard  and  leaves  them  to  germinate ;  or  when 
a  jaybird  flies  off  with  a  pecan  in  his  bill,  intending  to  crack 
and  eat  it,  but  accidentally  lets 
it  fall  where  it  will  sprout  and 
take  root.  Both  man  and  the 
lower  animals  are  not  only  in- 
voluntary, but  often  unwilling 
agents  of  dispersal.  Some  of  the 
most  troublesome  weeds  of  civili- 
zation have  been  unwittingly  dis- 
tributed by  man  as  he  journeyed 
from  place  to  place,  carrying, 
along  with  the  seed  for  planting 
his  crops,  the  various  weed  seeds, 
or  "screenings,"  as  these  mixtures 
are  called  by  dealers,  with  which 
they  have  been  adulterated  either  through  carelessness  and 
ignorance,  or  from  unavoidable  causes.  The  neglected 
animals,  also,  that  are  allowed  by  short-sighted  farmers  to 
wander  about  with  their  hair  full  of  cockleburs  and  other 


Fig.  39. — Dodder  on  red  clover, 
showing  how  the  seeds  get  mixed. 


24 


PRACTICAL  COURSE  IN  BOTANY 


adhesive  weed  pests,  are  no  doubt  very  unwilling  carriers  of 
those  disagreeable  burdens. 

21.  Tempting  the  appetite.  —  This  is  the  most  important 
adaptation  to  dispersal  by  animals.  Have  you  ever  asked 
yourself  how  it  could  profit  a  plant  to  tempt  birds  and  beasts 
to  devour  its  fruit,  as  so  many  of  the  bright  berries  we  find  in 
the  autumn  woods  seem  to  do?  To  answer  this  question, 
examine  the  edible  fruits  of  your  neighborhood  and  you  will 
find  that  almost  without  exception  the  seeds  are  hard  and 

bony,  and  either  too 
small  to  be  destroyed 
by  chewing,  and  thus 
capable  of  passing 
uninjured  through 
the  digestive  system 
of  an  animal ;  or,  if 
too  large  to  be  swal- 
lowed whole,  com- 
pelling the  animal, 
by  their  hardness  or 
disagreeable  flavor, 
to  reject  them.  In 
cases  where  the  seeds 
themselves  are  ed- 
ible and  attractive, 
the  fruits  are  usually 
armed  during  the 
growing  season  with 
protective  coverings, 
like  the  bur  of  the  chestnut  and  the  astringent  hulls  of  the  hick- 
ory nut  and  walnut.  The  acidity  or  other  disagreeable  quali- 
ties of  most  unripe  fruits  serves  a  similar  purpose,  while  their 
green  color,  by  making  them  inconspicuous  among  the  foliage 
leaves,  tends  still  further  to  insure  them  against  molestation. 

22.  Voluntary  agency.  —  The  cultivated  fruits  and  grains 
owe  their  distribution  and  survival  almost  entirely  to  the 


Figs.  40-42. — Adhesive  fruits  :  40,  fruit  of  hound's- 
tongue ;  41,  akene  of  bur  marigold ;  42,  fruit  of  bur 
grass  (cenchrus). 


THE  SEED 


25 


voluntary  agency  of  man.  Dispersal  by  this  means,  whether 
intentional  or  accidental,  is  purely  artificial,  and  except  in  the 
case  of  a  few  annuals  like  horseweed,  bitterweed,  ragweed, 
goosefoot,  and  other  field  pests  that  have  adjusted  their  sea- 
son of  growth  and  flowering  to  the  conditions  of  cultivation, 
is  not  correlated  with  any  special  modification  of  the  plants 
for  self-propagation.  On  the  contrary,  many  of  the  most 
widely  distributed  weeds  of  cultivation,  such  as  the  ox-eye 
daisy,  the  rib  grass,  mayweed  and  bitterweed,  possess  very 
imperfect  natural  means  of  dispersal,  and  are  largely  depend- 
ent for  their  propagation  on  the  involuntary  agency  of  man. 
23.  Use  of  the  fruit  in  dispersal.  —  It  will  be  seen  from  the 
foregoing  observations  that  the  fruit  plays  a  very  important 
part  in  the  work 
of  dispersal,  most 
of  the  adapta- 
tions for  this  pur- 
pose being  con- 
nected with  it. 
In  cases  where  a 
number  of  seeds 
are  contained 
in  a  large  pod 
that  could  not 
conveniently  be 
blown  about  by 
the  breeze, 
adaptations    for 

wind  dispersal  are  attached  to  the  individual  seeds,  as  in  the 
willow,  milkweed,  trumpet  creeper,  and  paulonia ;  but  as  a 
general  thing,  adaptations  of  the  seed  are  for  protection,  the 
work  of  dispersal  being  provided  for  by  the  fruit.  In  the  case 
of  the  large  class  of  plants  known  as  "  tumbleweeds,  "  the 
whole  plant  body  is  fitted  to  assist  in  the  work  of  transporta- 
tion. Such  plants  generally  grow  in  light  soils  and  either 
have  very  light  root  systems,  or  are  easily  broken  from  their 


.\\ir.i' 


'^ 


Fig.  43.  — A  fruiting  plant  of 
winged  pigweed  {Cycloloma), 
showing  the  bunchy  top  and  Fig.  44.  —  Panicle  ot 
weak  anchorage  of  a  typical  "old  witch  grass,"  a  coni- 
tumbleweed.  mon  tumbleweed. 


26 


PRACTICAL  COURSE   IN   BOTANY 


anchorage  and  left  to  drift  about  on  the  ground.  The  spread- 
ing, bushy  tops  become  very  light  after  fruiting,  so  as  to  be 
easily  blown  about  by  the  wind,  dropping  their  seeds  as  they 
go,  until  they  finally  get  stranded  in  ditches  and  fence  corners, 
where  they  often  accumulate  in  great  numbers  during  the 
autumn  and  winter. 

24.  The  advantages  of  dispersal.  —  Seed  cannot  germinate 
unless  they  are  placed  in  a  suitable  location  as  to  soil,  moisture, 
and  temperature.  In  order  to  increase  the  chances  of  secur- 
ing these  conditions,  it  is  clearly  to  the  advantage  of  a  species 
that  its  seeds  should  be  dispersed  as  widely  as  possible,  both 
that  the  seedlings  may  have  plenty  of  room,  and  that  they 
may  not  have  to  draw  their  nourishment  from  soil  already 
exhausted   by   their   parents.     The   farmer   recognizes   this 

principle  in  the  rotation  of 
crops,  because  he  knows  that 
successive  growths  of  the 
same  plant  will  soon  exhaust 
the  soil  of  the  substances  i*e- 
quired  for  its  nutrition,  while 
they  may  leave  it  richer  in 
nourishment  for  a  different 
crop. 

25.  Self-planting  seeds. — 
Dispersal  is  not  the  only 
problem  the  seed  has  to  meet. 
The  majority  of  seeds  cannot 
germinate  well  on  top  of  the 
ground,  and  must  depend  on 
various  agencies  for  getting 
under  the  soil.  Some  of  them 
do  this  for  themselves.  The 
seeds  of  the  stork's-bill,  popularly  known  as  ''filarees,"  have 
a  sharp-pointed  base  and  an  auger-shaped  appendage  at  the 
apex,  ending  in  a  projecting  arm  (the  ''  clock"  of  the  filaree) 
by  which  it  is  blown  about  by  the  wind  with  a  whirling  motion 


Fig.  45.  —  Self-planting  pod  of  peanut. 


THE   SKKD  27 

till  it  strikes  a  soft  spot,  when  it  begins  at  once  to  bore  its 
way  into  the  ground.  The  common  peanut  is  another  exam- 
ple. The  blossoms  are  borne  under  the  leaves,  near  the  base 
of  the  stem,  and  as  soon  as  the  seeds  begin  to  form,  the 
flower  stalks  lengthen  several  inches,  carrying  the  young  pods 
down  to  the  ground,  where  they  bore  into  the  soil  and  ripen 
their  seeds. 

Practical  Questions 

1.  Name  the  ten  most  troublesome  weeds  of  your  neighborhood. 

2.  What  natural  means  of  dispersal  have  they  ? 

3.  Which  of  them  owe  their  propagation  to  man  ? 

4.  Are  there  any  tumbleweeds  in  your  neighborhood  ? 

5.  Would  you  expect  to  find  such  weeds  in  a  hilly  or  a  well-wooded 
region?     (19,  23;  Exp.  17.) 

6.  What  situations  are  best  fitted  for  their  propagation?  (19,  23; 
Exp.  17.) 

7.  Make  a  list  of  all  the  fruits  and  seeds  you  can  think  of  that  are 
adapted  to  dispersal  by  wind ;  by  water ;  by  animals. 

8.  By  what  means  of  dissemination,  or  protection,  or  both,  is  each  of 
the  following  distinguished  :  the  squash;  apple;  fig;  pecan;  poppy; 
bean  ;  beggar-tick ;  linden ;  grape ;  rice ;  pepper ;  olive ;  cranberry ; 
jimsonweed;   thistle;   corn;   wheat;   oats? 

9.  What  is  the  agent  of  dispersion,  or  what  the  danger  to  be  provided 
against,  in  each  case  ? 

10.  Could  our  cultivated  fruits  and  grains  survive  in  their  present  state 
without  the  agency  of  man  ?     (22.) 

11.  Name  all  the  plants  you  can  think  of  that  bear  winged  seeds  and 
fruits ;  are  they,  as  a  general  thing,  tall  trees  and  shrubs,  or  low  herbs  ? 

12.  Name  all  you  can  think  of  that  bear  adhesive  seeds  and  fruits ;  are 
they  tall  trees  or  low  herbs  ? 

13.  Give  a  reason  for  the  difference.     (Exps.  17,  20.) 

14.  Why  is  the  dandelion  one  of  the  most  widely  distributed  weeds  in 
the  world?     (19;  Exp.  17.) 

15.  Is  the  wool  that  covers  cotton  seed  for  dispersal  or  protection  ? 

16.  What  advantage  to  the  Indian  shot  (canna)  is  the  excessive  hardness 
of  its  seeds?     (21.) 

17.  What  is  the  use  to  the  species,  of  the  bitter  taste  of  lemon  and 
orange  seed?     (21.) 

18.  Why  are  the  seeds  of  dates  and  persimmons  and  haws  so  hard? 
(21.) 


28  PRACTICAL  COURSE  IN  BOTANY 

1 9.  Do  you  find  any  edible  seeds  without  protection?  If  so,  account 
for  the  want  of  it.     (21,  22.) 

20.  Name  some  of  the  agencies  that  may  assist  in  covering  seeds  with 
earth. 

21.  Do  you  know  of  any  seeds  that  bury  themselves? 

22.  The  seeds  of  weeds  and  other  refuse  found  mixed  with  grain  sold 
on  the  market  are  known,  commercially,  as  "  screenings."  Wheat  brought 
to  mills  in  Detroit  showed  screenings  that  contained,  among  other  things, 
seeds  of  black  bindweed,  green  foxtail  grass,  yellow  foxtail,  chess,  oats, 
ragweed,  wild  mustard,  corn  cockle,  and  pigweed.  Can  you  mention  some 
of  the  ways  in  which  these  foreign  substances  may  have  gotten  into  the 
crop  and  suggest  means  for  keeping  them  out  ? 

Field  Work 

The  subjects  treated  in  the  foregoing  chapter  are,  in  general,  better 
suited  to  laboratory  than  to  field  work.  There  are  some  details,  however, 
which  can  be  observed  to  advantage  out  of  doors.  Many  of  the  seeds 
found  in  your  walks  will  show  peculiarities  of  shape  and  external  markings 
and  color  that  will  invite  observation.  Examine  also  the  contents  of  dif- 
ferent kinds  you  may  meet  with,  as  to  the  presence  or  absence  of  endosperm 
and  the  arrangement  and  development  of  the  embryo.  Note:  (1)  whether, 
as  a  general  thing,  there  is  any  difference  in  size  and  weight  and  amount  of 
nourishing  matter  in  the  two  kinds ;  (2)  the  greater  variety  in  the  shape 
and  arrangement  of  the  cotyledons  in  the  albuminous  kind,  and  in  the  ar- 
rangement of  the  embryo;  (3)  the  differences  in  the  development  of 
the  plumule  in  the  two  kinds,  —  and  give  a  reason  for  the  facts  observed. 

Among  the  different  seeds  you  may  find,  look  for  adaptations  for  dispersal, 
and  decide  to  what  particular  method  each  is  suited.  Study  the  agencies 
by  which  various  kinds  may  get  covered  with  soil.  If  the  common  stork's- 
bill  (Erodiutn  cicutarium)  grows  in  your  neighborhood,  its  seeds  will  well 
repay  a  little  study,  and  if  there  is  a  field  of  peanuts  within  reach,  do  not 
fail  to  pay  it  a  visit. 


CHAPTER   II.     GERMINATION   AND   GROWTH 
I.    PROCESSES  ACCOMPANYING  GERMINATION 

Material.  —  A  pint  or  two  of  corn,  peas,  beans,  or  any  quickly  germi- 
nating seed. 

Appliances.  —  Matches ;  wood  splinters ;  gas  jet  or  alcohol  lamp  ; 
test  tubes ;  a  small  quantity  of  mercuric  oxide ;  a  thermometer ;  a  couple 
of  two-quart  preserve  jars,  and  a  smaller  wide-mouthed  bottle  that  can 
be  put  into  one  of  them ;  some  limewater ;  a  glass  tube  (the  straws  used 
by  druggists  for  soft  drinks  will  answer). 

26.  Preliminary  exercises.  —  Before  taking  up  the  study 
of  germinating  seeds,  it  is  important  to  learn  from  what 
sources  the  organic  substances  used  by  the  growing  plant 
are  derived,  and  some  of  the  processes  that  accompany 
growth  and  development. 

Experiment  21.  To  show  the  changes  that  accompany  oxida- 
tion. —  Strike  a  match  and  let  it  burn  out.  Examine  the  burnt  portion 
remaining  in  your  hand ;  what  changes  do  you  notice  ?  These  changes 
have  been  caused  by  the  union  of  some  substance  in  the  match  with 
something  outside  of  it,  in  the  act  of  burning ;  let  us  see  if  we  can  find 
out  what  this  outside  substance  is. 

Experiment  22.  To  show  the  active  agent  in  oxidation.  — 
Heat  some  mercuric  oxide  in  a  test  tube  over  the  flame  of  a  burner. 
The  heat  will  cause  the  oxygen  to  separate  from  the  mercury,  and  in  a 
short  time  the  tube  will  be  filled  with  the  gas.  Extinguish  the  flame 
from  a  lighted  splinter  and  thrust  the  glowing  end  into  the  tube ;  what 
happens  ?  The  oxygen  unites  with  something  in  the  wood  and  causes  it  to 
burn  just  as  the  match  did.  Compare  your  burnt  splinter  with  the  burnt 
end  of  the  match ;   what  resemblance  do  you  notice  between  them  ? 

Experiment  23.  To  show  that  carbon  dioxide  is  a  product  of 
oxidation.  —  Your  experiment  with  the  match  showed  that  ignition 
is  accompanied  by  heat,  and  if  active  enough,  by  light,  and  also  that 
it  loft  behind  a  solid  substance  in  the  form  of  charcoal.  But  how 
about  the  part  that  united  with  the  oxygen  to  produce  these  results? 

29 


30 


PRACTICAL  COURSE  IN  BOTANY 


hand: 


Let  us  see  what  became  of  it.  Hold  a  lighted  candle  under  the  open  end 
of  a  test  tube,  or  under  the  mouth  of  a  small  glass  jar.  Does  any  vapor 
collect  on  the  inside  ?  After  two  or  three  minutes  quickly  invert  the  jar 
or  the  tul)e,  and  thrust  in  a  lighted  match :  what  happens  ?  Can  the 
substance  now  in  the  jar  be  ordinary  air?  Why  not?  (Exps.  21,  22.) 
Pour  in  a  small  quantity  of  limewater,  holding  your  hand  over  the  mouth 
of  the  tul)e  to  prevent  the  air  from  getting  in ;  the  gas  inside,  being  heavier 
than  air,  will  not  escape  inmiediately  unless  agitated.  What  change  do 
you  notice  in  the  limewater  ? 

It  has  been  proved  by  experiment  that  the  kind  of  gas  formed  by  the 
burning  candle  has  the  property  of  turning  limewater  milky;  hence, 
whenever  you  see  this  effect  produced  in  limewater,  you  may  conclude 
that  this  gas,  known  as  carbon  dioxide,  is  present;  and  conversely,  the 
presence  of  carbon  dioxide,  especially  if  accompanied  by  some  of  the  other 
effects  observed,  as  the  giving  out  of  heat  and  moisture,  may  be  taken  as 
evidence  that  some  process  similar  to  that  going  on  in  the  burning  candle 
is,  or  has  been,  at  work. 

Experiment  24.    Do  these  effects  accompany  any  of  the  life 
PROCESSES  OF  ANIMALS  ?  —  Blow  your  breath  against  the  palm  of  your 
what  sensation  do  you  feel  ?     Blow  it  against  a  mirror,  or  a  piece 
of  common  glass ;  what  do  you  see  ?    Blow  through  a 
tube  into  the  bottom  of  a  glass  containing  limewater ; 
^\        how  is  the  water  affected  ?     How  do  these  facts  cor- 
U      respond  with  the  results  of  Exp.  23  ? 

Experiment  25.     Is  there  any  evidence  that 

A  SIMILAR  PROCESS  GOES  ON  IN  PLANTS  ?  —  (1)  Half  fill 

a  small,  wide-mouthed  jar  with  limewater,  place  it  in- 

Syr^rvj,  side  a  larger  one  (Fig.  46),  and  fill  the  space  between 
^^W  them,  up  to  the  neck  of  the  smaller  vessel,  with  well- 
^^S  soaked  peas,  beans,  or  barleycorns,  on  a  bed  of  moist 
^^9  cotton  or  blotting  paper.  Cover  with  a  piece  of  glass 
.Kffisa  ^^^  j^ggp  .^^  .j^  moderately  warm  temperature.  (2)  As 
a  control  experiment,  place  beside  this  another  jar  ar- 
ranged in  precisely  the  same  way,  except  that  seeds 
must  be  used  whose  vitality  has  been  destroyed  by 
heat.  To  prevent  the  entrance  of  germs  among  the 
dead  seeds,  which  might  cause  fermentation  and  thus 
interfere  with  the  experiment,  set  the  jar  containing  them  in  a  vessel  of 
water  and  boil  an  hour  or  two  before  the  experiment  begins.  Otherwise, 
treat  precisely  as  in  (1). 

After  germination  has  taken  place  in  (1),  what  change  do  you  notice  in 
the  limewater  ?    If  the  effect  is  not  apparent,  gently  stir  with  a  straw  or 


r\ 


Fig.  46. —  Dia- 
grammatic section, 
showing  arrange- 
ment of  jars  for 
Exp.  25. 


GERMINATION  AND  GROWTH  31 

a  glass  rod  to  mix  it  with  the  gas  in  the  larger  jar.  Has  the  limewater  in 
the  control  experiment  undergone  the  same  change?  (It  may  show  a 
slight  niilkiness  due  to  the  carbon  dioxide  in  the  air.)  Insert  a  thermom- 
eter among  the  seeds  in  both  of  the  larger  jars,  and  compare  their  tem- 
perature with  that  of  the  outside  air;  which  shows  the  greater  rise? 
From  this  experiment  and  the  last  one,  what  process,  common  to  animals, 
would  you  conclude  has  been  going  on  in  the  germinating  seeds  ? 

Note.  —  Heat  in  germinating  seeds  is  not  always  due  to  this  cause 
alone,  but  is  sometimes  increased  by  the  presence  of  miimte  organisms 
called  bacteria.  Germinating  barley  and  rye  in  breweries  sometimes 
show  an  increase  in  temperature  of  40  to  70  degrees,  due  to  these  organisms, 
and  spontaneous  combustion  in  seed  cotton  has  been  reported  from  the 
same  cause. 

27.  Oxidation.  —  The  process  that  brought  about  the 
results  observed  in  the  foregoing  experiments,  and  popularly 
known  as  combustion,  is  more  accurately  defined  by  chemists 
as  oxidation.  It  takes  place  whenever  substances  enter  into 
new  combinations  with  oxygen.  The  most  familiar  examples 
of  it  are  when  oxygen  enters  into  combination  with  substances 
containing  carbon.  It  was  the  union  of  a  portion  of  the 
oxygen  of  the  air  in  Exp.  21,  and  of  that  in  the  tube  in  Exp. 
22,  with  some  of  the  carbon  in  the  wood,  that  caused  the 
burning.  The  effect  was  more  marked  in  the  second  case 
because  the  oxygen  in  the  tube  was  pure,  while  in  the  air  it 
is  mixed  with  other  substances. 

28.  Carbon.  —  The  black  substance  left  in  your  hand 
after  oxidation  of  the  wood  in  Exps.  21  and  22  is  carbon. 
It  composes  the  greater  part  of  most  plant  bodies,  and,  in 
fact,  is  the  most  important  element  in  the  realm  of  organic 
nature.  There  is  not  a  living  thing  known,  from  the  smallest 
microscopic  germ  to  the  most  gigantic  tree  in  existence,  that 
does  not  contain  carbon  as  one  of  its  essential  constituents. 

29.  Carbon  dioxide.  —  The  gas  produced  by  the  burning 
candle  in  Exp.  23,  by  the  germinating  seeds  in  Exp.  25,  and 
expelled  from  your  own  lungs  in  Exp.  24,  is  carbon  dioxide. 
Chemists  designate  it  by  the  symbol  CO2,  which  means  that 
it  consists  of  one  part  carbon  to  two  parts  oxygen.     It  is  ar 


32  PRACTICAL  COURSE  IN  BOTANY 

invariable  product  wherever  the  oxidation  of  substances 
containing  carbon  goes  on.  Heat  and  moisture  are  evolved 
at  the  same  time,  and  if  oxidation  is  very  active,  as  in  Exps. 
21  and  22,  light  also.  When  the  process  takes  place  very 
slowly,  no  light  is  evolved,  and  so  little  heat  as  to  be  imper- 
ceptible without  special  observation.  Hence,  oxidation  may 
go  on  around  us  and  even  in  our  own  bodies  without  our 
being  conscious  of  the  fact. 

Carbon  dioxide  is  of  prime  importance  to  the  well-being  of 
plants.  It  furnishes  the  material  from  which  the  greater 
part  of  their  organic  food  is  derived,  as  will  be  seen  when 
we  take  up  the  study  of  the  leaf  and  its  work.  To  animals, 
on  the  contrary,  its  presence  is  so  injurious  that  if  the  pro- 
portion of  it  in  the  air  we  breathe  ever  rises  much  above  1 
part  to  1000,  the  ill  effects  become  painfully  sensible.  It 
is  not,  however,  as  was  formerly  supposed,  a  poison,  the 
harm  it  does  being  to  decrease  the  proportion  of  oxygen 
in  the  atmosphere  so  that  animals  cannot  get  enough  of  it 
to  breathe,  and  die  of  suffocation. 

30.  Respiration  in  plants  and  in  animals.  —  It  was  shown 
in  Exp.  24  that  respiration  in  animals  is  accompanied  by  the 
products  of  oxidation;  hence  we  conclude  that  respiration 
is  a  form  of  oxidation.  And  since  these  same  products  are 
given  off  by  plants  (Exp.  25),  the  inference  is  clear  that  the 
same  process  goes  on  in  them.  But  in  plants  the  life  func- 
tions are  so  much  more  sluggish  than  in  animals  that  it  is 
only  in  their  most  active  state,  during  germination  and 
flowering,  that  evidence  of  it  is  to  be  looked  for. 

31.  Respiration  and  energy.  —  In  plants,  as  in  animals, 
respiration  is  the  expression  or  measure  of  energy.  Sleeping 
animals  breathe  more  slowly  than  waking  ones,  snakes  and 
tortoises  more  slowly  than  hares  and  hawks.  The  more 
we  exert  ourselves  and  the  more  vital  force  we  expend,  the 
harder  we  breathe ;  hence,  respiration  is  more  active  in 
children  than  in  older  persons  and  in  working  people  than  in 
those  at  rest,    It  i§  the  same  with  plants ;  respiration  is  most 


GERMINATION  AND  GROWTH  33 

perceptible  in  germinating  seeds  and  young  leaves,  in  buds 
and  flowers,  where  active  work  is  going  on.  Hence,  in  this 
condition  they  consume  proportionately  larger  quantities 
of  oxygen  and  liberate  correspondingly  larger  quantities  of 
carbon  dioxide,  with  a  proportionate  increase  of  heat.  In 
some  of  the  arums,  —  calla  lily,  Jack-in-the-pulpit,  colo- 
casia,  etc.,  —  and  in  large  heads  of  compositse,  like  the  sun- 
flower, where  a  great  number  of  small  flowers  are  brought 
together  within  the  same  protecting  envelope,  the  rise  of 
temperature  is  sometimes  so  marked  that  it  may  be  per- 
ceived by  placing  a  flower  cluster  against  the  cheek. 

Practical  Questions 

1.  What  is  charcoal  ?     (28.) 

2.  Is  any  of  this  substance  contained  in  the  seed?  in  the  flour  and 
meal  made  from  seed?     (28;  Exp.  25.) 

3.  What  combination  takes  place  when  the  cook  lets  the  stove  get  too 
hot  and  burns  the  biscuits?     (27,  28.) 

4.  Of  what  does  the  burned  part  consist?  (28.)  What  was  it  before 
it  was  burned?     (27,28). 

5.  Which  burns  the  more  readily,  an  oily  seed  or  a  starchy  one? 
Which  leaves  the  more  solid  matter  behind  ?  (Suggestion :  test  by  put- 
ting a  bean,  or  a  large  grain  of  corn,  and  an  equal  quantity  of  the  kernel 
of  a  Brazil  nut  on  the  end  of  apiece  of  wire  and  thrusting  into  a  flame.) 

6.  Is  there  any  rational  ground  for  the  statement  that  the  wooden 
buildings  formerly  used  on  Southern  plantations  as  cotton  ginneries  were 
sometimes  destroyed  through  spontaneous  combustion  due  to  the  heat 
generated  by  piles  of  decaying  cotton  seed  ?     (Exp.  25,  Note.) 

n.     CONDITIONS   OF  GERMINATION 

Material.  —  Several  ounces  each  of  various  kinds  of  seed.  For  the 
softer  kinds,  pea,  bean,  corn,  oats,  wheat  are  recommended ;  for  those 
with  harder  coverings,  squash,  castor  bean,  apple,  pear,  or,  where  ob- 
tainable, cotton ;  for  still  harder  kinds,  persimmon  and  date  seeds,  or  the 
stones  of  plum  and  cherry. 

Appliances.  —  1  dozen  common  earthenware  plates  for  germinators ; 
1  dozen  two-ounce  wide-mouthed  bottles;  2  common  glass  tumblers; 
clean  sand,  sawdust,  or  cotton  batting,  for  bedding ;  a  double  boiler ;  a 
gas  burner,  or  a  lamp  stove. 


34 


PRACTICAL   COURSE   IN  BOTANY 


32.  Recording  observations.  —  For  this  purpose  a  page 
should  be  ruled  off  in  the  notebook  of  each  student,  after 
the  model  here  given,  and  the  facts  brought  out  by  the  differ- 
ent experiments  set  down  as  observed. 

Number  of  Seeds  Germinated 


No.  of  hoizrs  . . 

24 

48 

72 

4d. 

5d. 

6d. 

7d. 

8d. 

10  d. 

No.  of  vessel . . 

1 

No.  of  vessel . . 

2 

No.  of  vessel . . 

3 

No.  of  vessel.  . 

4 
5 

No.  of  vessel .  . 

No.  of  vessel. . 

6 

Experiment  26.  Can  seeds  have  too  much  moisture  ?  —  Drop  a 
number  of  dry  beans  or  grains  of  corn,  oats,  or  other  convenient  seed, 
into  a  vessel  with  a  bedding  of  cotton  or  paper  that  is  barely  moistened, 
and  an  equal  number  of  soaked  seeds  of  the  same  kind  into  another  vessel 
with  a  saturated  bedding  of  the  same  material.  In  a  third  vessel  place 
the  same  number  of  soaked  seed,  covering  them  partially  with  water,  and 
in  a  fourth  cover  the  same  number  entirely.  Label  them  1,  2,  3,  and  4; 
keep  all  together  in  a  warm,  even  temperature,  and  observe  at  intervals 
of  twenty-four  hours  for  a  week.  What  condition  as  to  moisture  do 
you  find  most  favorable  to  germination  ?  Would  seeds  germinate  in  the 
entire  absence  of  moisture  ?     How  do  you  know  ? 

Experiment  27.  Was  it  the  presence  of  too  much  water,  or 
the  lack  of  air  caused  by  it,  that  interfered  with  germination 
IN  THE  LAST  EXPERIMENT? — To  answer  this  question  experimentally  is 
not  easy,  since  it  is  difficult  to  obtain  a  complete  vacuum  without  special 
appliances.  The  simplest  way  is  to  fill  with  mercury  a  glass  tube  30 
inches  long,  closed  at  one  end,  and  invert  it  over  a  small  vessel  —  a  tea- 
cup, or  an  egg  cup  will  answer  —  containing  mercury  enough  to  cover 
the  bottom  to  a  depth  of  two  or  three  centimeters  (see  Appendix,  Weights 
and  Measures,  for  English  equivalents.)  The  tube  must  be  supported  in 
such  a  way  that  its  lower  end  will  dip  into  the  mercury  without  touching 
the  bottom  of  the  vessel.  With  a  pair  of  forceps  insert  under  the  mouth  of 
the  tube  two  or  three  seeds  that  have  been  well  soaked  in  water  deprived 
of  air  by  previous  boiling.  Being  lighter  than  mercury,  they  will  float  to 
the  top,  where  there  is  a  complete  absence  of  air  while  other  conditions 


GERMINATION  AND  GROWTH 


35 


favorable  to  germination  are  present.  Before  releasing,  they  should  be 
well  shaken  under  the  mercury  to  free  them  from  air  bubbles,  and  if  the 
coats  are  loose  fitting  so  that  they  can  be  removed  without  injury  to  the 
parts  inclosed  in  them,  they  should  be  slipped  off  in  order  to  get  rid  of  any 
imprisoned  air  they  may  contain.  Additional  moisture  may  be  supplied, 
if  necessary,  by  injecting,  by  means  of  a  medicine  dropper  inserted  under 
the  mouth  of  the  tube,  a  drop  or  two  of  water  that  has  been  previously 
boiled.  Keep  in  a  warm,  even  temperature,  under  conditions  favorable 
to  germination,  and  compare  the  behavior  of  the  seeds  with  those  placed 
in  the  different  vessels  in  Exp.  26. 

If  appliances  for  this  experiment  are  lacking,  a  rough  approximation 
can  be  made  by  using  the  seeds  of  aquatic  plants,  such  as  the  lotus,  water 
lily,  and  the  so-called  Chinese  sacred  bean,  sold  in  the  variety  stores, 
which  we  know  are  capable  of  germinating  in  the  limited  amount  of  air 
contained  in  ordinary  soil  water.  Place  an  equal  number  of  such  seeds, 
of  about  the  same  size  and  weight,  on  a  bedding  of  common  garden  soil 
in  two  glass  tumblers.  Fill  one  vessel  a  Uttle  over  half  full  of  ordinary 
soil  water  and  the  other  to  the  same  height  with 
water  from  which  the  air  has  been  expelled  by  boil- 
ing. Pour  over  the  liquid  a  film  of  sweet  oil  or  castor 
oil,  to  prevent  the  access  of  air,  leaving  the  surface  of 
the  water  in  the  other  vessel  exposed.  In  which  do 
the  seeds  come  up  most  freely  ? 

Some  seeds,  especially  those  rich  in  proteins,  as 
peas  and  beans,  will  germinate  in  a  vacuum,  because 
oxygen  is  supplied  for  a  time  by  the  chemical  decom- 
position of  substances  in  their  tissues  which  contain  it, 
but  when  these  are  exhausted,  respiration  ceases  and 
death  ensues. 


Experiment  28.  Does  the  depth  at  which  seeds 

ARE  PLANTED  AFFECT  THEIR  GERMINATION  ?  —  Plant  a 

number  of  peas  or  grains  of  corn  at  different  depths 
in  a  wide-mouthed  glass  jar  filled  with  moist  sand,  as 
shown  in  Fig.  47,  the  lowest  ones  at  the  bottom,  the 
top  ones  barely  covered.  Try  different  kinds  of  seed 
and  grain,  —  radish,  squash,  cotton,  or  wheat,  —  and 
watch  them  make  their  way  to  the  surface.  Do  you 
notice  any  difference  in  this  respect  between  large 
seed  and  small  ones  ?  Between  those  with  thick  coty- 
ledons and  thin  ones  ?  At  what  depth  do  you  find, 
from  your  recorded  observations,  that  seed  germinate 
best?" 


Fig.  47.  — To  find 
out  the  proper  depth 
at  which    to   plant 


36 


PRACTICAL  COURSE  IN  BOTANY 


Experiment  29.  What  temperature  is  most  favorable  to  germi« 
NATION  ?  —  Put  half  a  dozen  soaked  beans  on  moist  cotton  or  sawdust  in 
three  wide-mouthed  bottles  of  the  same  size  or  in  germinators  arranged  as 
in  Figs.  48,  49,  the  seed  also  being  selected 
with  a  view  to  similarity  of  size  and  weight. 
Keep  one  at  a  freezing  temperature ;  the 
second  in  a  temperature  of  15°  to  20°  C. 
(see  Appendi.x  for  Fahrenheit  equivalents) ; 
and  the  third,  at  30°  C.  If  a  place  can 
be  found  near  a  stove  or  a  register,  where 
an  even  temperature  of  about  125°  F. 
is  maintained,  place  a  fourth  receptacle 
there.  Observe  at  intervals  of  twenty- 
four  hours  for  a  week  or  ten  days,  keeping 
the  temperature  as  even  as  possible,  and 
maintaining  an  equal  quantity  of  moisture 
in  each  vessel.  Make  a  daily  record  of 
your  observations.  What  temperature  do 
you  find  most  favorable  to  germination  ? 


Figs.  48,49.— Home-made  ger- 
minators :  48,  closed  ;  49,  showing 
interior  arrangement. 


Experiment  30.  At  what  temperature  do  seeds  lose  their  vital- 
ity ?  —  Place  about  two  dozen  each  of  grains  of  corn,  beans,  squash 
seed,  and  castor  beans,  with  an  equal  number  of  plum  or  cherry  stones, 
in  water,  and  heat  to  a  temperature  of  150°  F.  After  an  exposure  of 
ten  minutes,  take  out -six  of  each  kind  and  place  in  germinators  made 
of  two  plates  with  moist  sand  or  damp  cloth  between  them,  as  shown 
in  Figs.  48,  49.  Raise  the  temperature  to  175°  F.,  and  after  ten  minutes 
take  out  six  more  of  each  kind  of  seed  and  j^lace  in  another  germinator. 
Raise  the  water  in  the  vessel  to  200°,  take  out  another  batch  of  seeds; 
raise  to  the  boiling  point  for  ten  minutes  more,  and  plant  the  remain- 
ing six  of  each  lot.  Number  the  four  germinators,  and  observe  at  in- 
tervals of  twenty-four  hours  for  two  weeks.  The  harder  kinds  should  be 
kept  under  observation  for  three  or  four  weeks,  as  they  germinate  slowly. 

Try  the  same  experiments  with  the  same  kinds  of  seeds  at  a  dry  heat, 
using  a  double  boiler  to  prevent  scorching,  and  record  observations  as  before. 

Experiment  31.  Time  required  for  germination.  —  Arrange  in 
germinators  seeds  of  various  kinds,  such  as  corn,  wheat,  peas,  turnip,  apple, 
orange,  grape,  castor  bean,  etc.  "Clip"  some  of  the  harder  ones  and  keep 
all  the  kinds  experimented  with  under  similar  conditions  as  to  moisture, 
temperature,  (^tc,  and  record  the  time  required  for  each  to  sprout.  What 
is  the  effect  of  clijiping,  and  why  ? 

Experiment  32.  Are  very  young  or  immature  seeds  capable  of 
GERMINATING  ?  —  Plant  some  seeds  from  half-grown  tomatoes,  and  grains 


GERMINATION   AND  GROWTH 


37 


of  wheat,  oats,  or  barley  before  they  are  ready  for  harvesting.  Try  as 
many  kinds  as  you  like,  and  see  how  many  will  come  up.  Notice  whether 
there  is  any  difference  in  the  health  and  vigor  of  plants  raised  from  seeds 
in  different  stages  of  maturity. 

Experiment  33.  The  relative  value  of  perfect  and  inferior 
SEED.  —  From  a  number  of  seeds  of  the  same  species  select  half  a  dozen  of 
the  largest,  heaviest, 
and  most  perfect,  and 
an  equal  number  of 
small,  inferior  ones.  If 
a  pair  of  scales  is  at 
hand,  the  different  sets 
should  be  weighed  and 
a  record  kept  for  com- 
parison with  the  seed- 
lings at  the  end  of  the 
experiment.  Plant  the 
two  sets  in  pots  con- 
taining exactly  the 
same  kind  of  soil,  and 
keep  under  identical 
conditions  as  to  light, 
temperature,  and 
moisture.  Keep  the 
seedlings  under  obser- 
vation for  two  or  three 
weeks,  making  daily 
notes  and  occasional 
drawings  of  the  height 
and  size  of  the  stems, 
and  the  number  of 
leaves  produced  by 
each. 

33.  Resistance 
to  heat  and  cold. — 
In  making  experi- 
ments with  regard  to  temperature,  notice  how  the  extremes 
tolerated  are  influenced,  first,  by  the  length  of  time  the 
seeds  are  exposed ;  second,  by  the  amount  of  water  contained 
in  them ;  and  third,  by  the  nature  of  the  seed  coats.  Every 
fanner  knows  that  the  effect  of  freezing  is  much  more  in- 


50 

Figs.  50,  51.  —  Stem  development  of  seedlings:  50, 
raised  from  healthy  grains  of  barley ;  weight,  39.5 
grams  (about  500  grs.)  ;  51,  raised  under  exactly  similar 
conditions  from  the  same  number  of  inferior  grains ; 
weight,  23  grams  (about  350  grs.). 


52  53 

Figs.  52,  53.  —  Improvement  of  corn  by  selection  : 
62,  original  type;  53,  improved  type  developed  from  it. 


38  PRACTICAL  COURSE   IN   BOTANY 

jurious  to  plants  or  parts  of  plants  when  full  of  sap  (water) 
than  when  dry.  This,  in  the  opinion  of  the  most  recent 
investigators,  is  because  the  water  in  the  spaces  outside  the 
cells  freezes  first  and  as  moisture  is  gradually  withdrawn 
from  the  inside  to  take  its  place,  the  soluble  salts  which  may 
be  present  in  the  cell  sap  become  more  concentrated,  and  by 
their  chemical  action  on  the  contained  proteins  cause  them 
to  be  precipitated,  or  "  salted  out,"  as  we  see  sugar  or  salt 
precipitated  from  solutions  of  those  substances  when  water 
is  withdrawn  by  evaporation.  In  this  way,  it  is  believed, 
the  fundamental  protoplasm  of  the  cell  may  be  so  disorganized 
that  death  ensues  if  the  freezing  is  continued  long  enough, 
since  the  protein  precipitates  become  "  denatured  "  and  cannot 
be  reabsorbed  if  kept  in  a  solid  state  too  long.  The  length  of 
time  necessary  to  produce  death  from  this  cause  is,  of  course, 
different  in  different  plants,  according  to  the  kind  of  salts 
dissolved  in  the  sap  and  the  nature  of  the  proteins  acted  on 
by  them.  The  proteins  in  the  sap  of  Begonia,  or  Pelargo- 
nium, plants  which  are  very  sensitive  to  cold,  yield  a  dena- 
tured precipitate  at,  or  a  little  below  the  freezing  point  of 
water,  while  those  of  winter  rye  withstand  a  temperature  of 
-15°  C,  and  of  pine  needles,  -40°  C. 

Mechanical  injury  through  rupture  of  parts  by  freezing 
is  not  apt  to  cause  serious  damage  except  in  cases  of  sudden 
and  violent  cold  at  a  time  when  the  tissues  are  gorged  with 
sap,  as  not  infrequently  happens  during  the  abrupt  changes 
of  temperature  which  sometimes  occur  in  spring  after  the 
trees  have  put  forth  their  leaves.  In  an  extreme  case  of 
this  kind,  the  writer  has  seen  the  trunk  of  an  oak  a  foot 
or  more  in  diameter  split  in  deep  seams  from  the  effects 
of  freezing. 

34.  The  length  of  time  during  which  seeds  may  retain 
their  vitality.  —  No  direct  experiment  can  be  made  to  test 
this  point,  since  it  would  require  months,  or  even  years, 
covering  in  some  instances  more  than  the  lifetime  of  a  genera- 
tion.    It  has  been  stated  on  good  authority  that  seeds  of  the 


GERMINATION  AND  GROWTH  39 

water  chinquapin  (Nelumbo)  have  germinated  after  more 
than  a  hundred  years,  and  moss  spores  preserved  in  her- 
bariums, after  fifty.  But  the  records  in  such  cases  are  not 
always  trustworthy,  and  there  is  absolutely  no  foundation 
for  the  statements  sometimes  made  about  the  germination 
of  wheat  grains  found  preserved  with  mummies  over  two 
thousand  years  old.  If  kept  perfectly  dry,  however,  seed 
may  sometimes  be  preserved  for  months,  or  even  years. 
Peas  have  been  known  to  sprout  after  ten  years,  red  clover 
after  twelve,  and  tobacco  after  twenty.  Ordinarily,  however, 
the  vitality  of  seeds  diminishes  with  age,  and  in  making  ex- 
periments it  is  best  to  select  fresh  ones.  Those  used  for 
comparison  should  also,  as  far  as  possible,  be  of  the  same  size 
and  weight. 

35.  Effect  of  precocious  germination.  —  It  has  been  found 
by  experiment  that  plants  raised  from  immature  seed,  when 
they  will  germinate  at  all  (Exp.  32),  yield  earlier  and  larger 
crops  than  the  same  kinds  from  mature  seed.  Early  toma- 
toes and  some  other  vegetables  are  produced  in  this  way. 
The  majority  of  seeds,  however,  require  a  period  of  rest 
before  beginning  their  life  work.  Those  that  are  forced  to 
take  up  the  burden  of  "  child  labor  "  show  the  effect  of 
such  abnormal  condition  by  yielding  fruits  that  are  smaller 
and  less  firm  than  those  raised  from  mature  seed,  so  that 
they  do  not  keep  well  and  have  to  be  marketed  quickly. 
Under  what  circimastances  does  it  pay  to  cultivate  such 
fruits? 

Practical  Questions 

1.  What  are  the  principal  external  conditions  that  affect  germination? 
(Exps.  26-29.) 

2.  What  effect  has  cold  ?  want  of  air  ?  too  much  water  ? 

3.  Is  light  necessary  to  germination  ? 

4.  What  is  the  use  of  clipping  seeds?  (Kxps.  12,  13,  14,  and  Material, 
p.  12.) 

5.  In  what  cases  should  it  be  resorted  to?     (Exp.  31.) 

6.  Why  will   seed  not   germinate  in   hard,  sun-baked  land  without 


40  PRACTICAL  COURSE  IN  BOTANY 

abundant  tillage  ?     Why  not  on  undrained  or  badly  drained  land  ?     (Exps. 
26,  27.) 

7.  Will  seeds  that  have  lost  their  vitality  swell  when  soaked?  (Exp.  16. ) 

8.  Are  there  any  grounds  for  the  statement  that  the  seeds  of  plums 
boiled  into  jam  have  sometimes  been  known  to  germinate  ?  ^    (."53;  Kxp.  30.) 

9.  Could  such  a  thing  happen  in  the  case  of  apple  or  sunflower  seed, 
and  why  or  why  not  ?     (33.) 

10.  Does  it  make  any  difference  in  the  health  and  vigor  of  a  plant 
whether  it  is  grown  from  a  large  and  well-developed  seed  or  from  a  weak 
and  puny  one?     (Exp.  33.) 

11.  Would  a  farmer  be  wise  who  should  market  all  his  best  grain  and 
keep  only  the  inferior  for  seed  ? 

12.  What  would  be  the  result  of  repeated  plantings  from  the  worst 
seed? 

13.  Of  constantly  replanting  the  best  and  most  vigorous  ? 

14.  Suppose  seed  would  germinate  without  moisture;  would  this  be 
an  advantage,  or  a  disadvantage  to  agriculturists  ? 

15.  Why  is  a  cool,  dry  place  best  for  keeping  seeds  ?     (Exps.  26,  29.) 

16.  Why  are  the  earliest  tomatoes  found  in  the  market  usually  smaller 
than  those  off ered  later  ?     (35.) 

17.  Why  is  continued  rain  so  Injurious  to  wheat,  oats,  and  other  grains 
before  they  are  mature  enough  to  be  harvested?     (35;  Exp.  32.) 

18.  Would  the  same  effect  be  likely  to  occur  in  the  case  of  very  oily 
seeds,  such  as  flax  and  castor  beans  ?  Why  ?  (Suggestion  :  try  the  effect 
of  putting  water  on  a  piece  of  oiled  paper.) 

19.  Explain  why  many  seeds  cannot  germinate  successfully  without 
air.     (30,  31;  Exp.  25.) 

20.  Mention  some  of  the  practical  advantages  that  a  farmer,  a  gardener, 
or  a  careful  housewife  might  gain  from  experiments  like  those  made  in  this 
section. 

21.  Explain  why  seeds  can  endure  so  much  greater  extremes  of  tempera- 
ture than  growing  plants.     (23,  33.) 


m.    DEVELOPMENT   OF  THE   SEEDLING 

Material.  —  Seedlings  of  various  kinds  in  different  stages  of  growth. 
It  is  recommended  that  the  same  species  be  used  that  were  studied  in 
Section  III,  Chapter  I,  or  such  equivalents  as  may  have  been  substituted 
for  them.  Enough  should  be  provided  to  give  each  pupil  three  or  four 
specimens  in  different  stages  of  development.    Seeds,  even  of  the  same  kind, 

1  Vines,  "  Lectures  on  the  Physiology  of  Plant?,"  p.  282.  See  also  Sachs, 
*' Physiology  of  Plants." 


GERMINATION  AND  GROWTH 


41 


develop  at  such  different  rates  that  it  will  probably  not  be  necessary  to 
make  more  than  two  plantings  of  each  sort,  from  2  to  5  days  apart. 
Soaked  seeds  of  corn  and  wheat  will  germinate  in  from  3  to  7  days, 
according  to  the  temperature;  oats  in  1  to  4;  beans  in  4  to  6; 
squash  and  castor  beans  in  from  8  to  10.  Very  obdurate  ones  may 
be  hastened  by  clipping.  Keep  the  germinators  in  an  even  temperature, 
at  about  70°  to  80°  F. 

Pine  is  a  very  difficult  seed  to  germinate,  requiring  usually  from  18  to  21 
days.  By  soaking  the  mast  for  twenty-four  hours  and  planting  in  damp 
sand  or  sawdust  kept  at  an  even  temperature  of  23°  C.  or  about  75°  F., 
specimens  may  be  obtained. 


L 


36.  Seedlings  of  monocotyls.  —  Examine  a  seedling  of 
corn  that  has  just  begun  to  sprout ;  from  which  side  does  the 
seedhng  spring,  the  plain  or  the  grooved  one  ?  Refer  to  your 
sketch  of  the  dry  grain  and  see   if  this 

agrees  with  the  position  of  the  embryo  as 
observed  in  the  seed.  Make  sketches  of 
four  or  five  seedlings  in  different  stages  of 
advancement,  until  you  reach  one  with  a 
well-developed  blade.  From  what  part  of 
the  embryo  has  each  part  of  the  seedling 
developed?  Which  part  first  appeared 
above  ground?  Is  it  straight,  or  bent  in 
any  way?  In  what  direction  does  the 
plumule  grow  ?  The  hypocotyl  ?  Does  the 
cotyledon  appear  above  ground  at  all?  Slip 
off  the  husk  and  see  if  there  is  any  differ- 
ence in  the  size  and  appearance  of  the 
contents  as  you  proceed  from  the  younger 
to  the  older  plants.  How  would  you  ac- 
count for  the  difference? 

37.  The  root.  —  Examine  the  lower  end  of  the  hypocotyl 
and  find  where  the  roots  originate  ;  would  you  say  that  they 
are  an  outgrowth  from  the  stem,  or  the  stem  from  the  root  ? 
Observe  that  the  root  of  the  corn  does  not  continue  to  grow 
in  a  single  main  axis  like  that  of  the  castor  bean,  but  that 
numerous  adventitious  and    secondary  roots  spring  from 


Figs.  54,  55.— Seed- 
ling of  corn  {after 
Gray)  :  54,  early  stage 
of  germination ;  55, 
later  stage. 


42 


PRACTICAL  COURSE  IN  BOTANY 


various  ])oints  near  the  base  of  the  hypocotyl  and  spread  out 
in  every  direction,  thus  giving  rise  to  the  fibrous  roots  of 
grains  and  grasses. 

38.  Root  hairs.  —  Notice  the  grains  of  sand  or  sawdust 
that  cHng  to  the  rootlets  of  plants  grown  in  a  bedding  of  that 

kind.  Examine  with  a  lens  and  see  if  you 
can  account  for  their  presence.  Lay  the  root 
in  water  on  a  bit  of  glass,  hold  up  to  the  light 
and  look  for  root  hairs  ;  on  what  part  are  they 
most  abundant? 

The  hairs  are  the  chief  agents  in  absorbing 
moisture  from   the  soil.     They  do  not  last 
very  long,  but  are  constantly  dying  and  being 
renewed  in  the  younger  and  tenderer  parts  of 
Fig.  56.  —  Seed-  the  root.     These  are  usually  broken  away  in 

ling  of  wheat,  with  tearing  the  roots  from  the  soil,  so  that  it  is  not 
easy  to  detect  the  hairs  except  in  seedlings, 

even  with  a  microscope.     In  oat,  maple,  and  radish  seedlings 

they  are  very  abundant  and  clearly  visible  to  the  naked  eye. 

The  amount  of  absorbing  surface  on  a 

root  is  greatly  increased  by  their  presence. 

39.  The  root  cap.  —  Look  at  the  tip  of 
the  root  through  your  lens  and  notice  the 
soft,  transparent  crescent  or  horseshoe- 
shaped  mass  in  which  it  terminates.  This 
is  the  root  cap  and  serves  to  protect  the 
tender  parts  behind  it  as  the  roots  burrow 
their  way  through  the  soil.  Being  soft 
and  yielding,  it  is  not  so  likely  to  be  in- 
jured by  the  hard  substances  with  which 
it  comes  in  contact  as  would  be  the  more 
compact  tissue  of  the  roots.  It  is  composed 
of  loose  cells  out  of  which  the  solid  root 
substance  is  being  formed;  the  growing  point  of  the  root, 
g,  is  at  the  extremity  of  the  tip  just  behind  the  cap,  c  (Fig.  57). 
The  cap  is  very  apparent  in  a  seedling  of  corn,  and  can  easily 


Fig.  57.  —  Diagram- 
matic section  of  a  root 
tip  :  a,  cortex  ;  h,  central 
cylinder  in  which  the 
conducting  vessels  are 
situated  ;  c,  root  cap  ;  g, 
growing  point. 


GERMINATION  AND  GROWTH 


43 


be  seen  with  the  naked  eye,  especially  if  a  thin  longitudinal 
section  is  made.  It  is  also  well  seen  in  the  water  roots  of  the 
common  duckweed  {Lemna),  and  on  those  developed  by  a 
cutting  of  the  wandering  Jew,  when  placed  in  water.  Are 
there  any  hairs  on  the  root  cap  ?  Can  you  account  for  their 
absence  ? 

Note.  — For  a  minute  study  of  the  structure  of  roots,  see  67. 

40.  Organs  of  vegetation.  —  The  three  parts,  root,  stem, 
and  leaf,  are  called  organs  of  vegetation  in  contradistinction  to 
the  flower  and  fruit,  which  constitute 
the  organs  of  reproduction.  The  for- 
mer serve  to  maintain  the  plant's  indi- 
vidual existence,  the  latter  to  produce 
seed  for  the  propagation  of  the  species, 
so  we  find  that  the  seed  is  both  the  be- 
ginning and  the  end  of  vegetable  life. 

41 .  Definitions. — Organ  is  a  general 
name  for  any  part  of  a  living  thing, 
whether  animal  or  vegetable,  set  apart 
to  do  a  certain  work,  as  the  heart  for 
pumping  blood,  or  the  stem  and  leaves 


Fig.  58. — Seedlings  of  bean 
in  different  stages  of  growth  : 
cc,  cotyledons,  showing  the 
plumule  and  hypocotyl  before 


of  a  plant  for  conveying  and  digesting   germination;  a,  b  d,  and  e, 

•^  .  .  successive  stages  of  advance- 

Sap.       By    "  function  "    is    meant    the    ment.    At  d  the  arch  of  the 

particular  work  or  office  that  an  organ   ^SS£ ,  j,  .Stf  Jy 

has  to  perform.  erected  itself. 

42.  Seedlings  of  dicotyls.  The  bean.  —  Sketch,  with- 
out removing  it,  a  bean  seedling  that  has  just  begun  to  show 
itself  above  ground ;  what  part  is  it  that  protrudes  first  ? 
Sketch  in  succession  four  or  five  others  in  different  stages  of 
advancement.  Notice  how  the  hypocotyl  is  arched  where 
it  breaks  through  the  soil.  Does  this  occur  in  the  monocotyl? 
examined?  Do  the  cotyledons  of  the  bean  appear  above 
ground?  How  do  they  get  out?  Can  you  perceive  any 
advantage  in  their  being  dragged  out  of  the  ground  back- 
wards in  this  way  rather  than  pushed  up  tip  foremost? 


44 


PRACTICAL  COURSE  IN  BOTANY 


WTiat  changes  have  the  cotyledons  undergone  in  the  suc- 
cessive seedUngs?  Remove  from  the  earth  a  seedling  just 
l)eginuing  to  sprout  and  sketch  it.  From  what  point  does 
the  h ypocotyl  protrude  through  the  coats  ?  Does  this  agree 
with  its  position  as  sketched  in  your  study  of  the  seed? 
In  which  part  of  the  embryo  does  the  first  growth  take  place? 

Remove  in  succession  the  several  seedlings  you  have 
sketched  and  note  their  changes.  How  does  the  root  differ 
from  that  of  the  corn  and  oats  ?  The  first  root  formed  by  the 
extension  of  the  hypocotyl  is  the  primary  root  and  should  be 
so  labeled  in  your  drawings ;  the  branches  that  spring  from 
it  are  secondary  roots.  Look  for  root  hairs;  if  there  are 
any,  where  do  they  occur? 

43.  Germination  of  the  squash.  —  How^  does  the  manner 
of  breaking  through  the  soil  compare  with  that  of  the  bean  ? 


Co 


e  c  b  a 

Fig.  59.  —  Stages  in  the  germination  of  a  typical  seedling  of  the  squash  family : 
z,  a  seed  before  germination  ;  b,  c,  e,  the  same  in  different  stages  of  growth  ;  d,  the 
empty  testa,  with  kernel  removed  ;  hi,  hilum  ;  m,  micropjde  ;  p,  p,  the  peg  in  the  heel ; 
h,  h,  h,  the  hypocotyl ;  (ir,  arch  of  the  hypocotyl ;  co,  cotyledons ;  pi,  plumule ;  ^jr, 
primary  root ;  sc,  secondary  roots. 

With  the  corn?  From  which  end  of  the  seed,  the  large  or 
the  small  one,  does  the  hypocotyl  spring  ?  Do  the  cotyledons 
come  above  ground  ?  How  do  they  get  out  of  the  seed  coat  ? 
Notice  the  thick  protuberance  developed  by  the  hypocotyl 
and  pressing  against  the  lower  half  of  the  coat  at  the  point 
where  the  hypocotyl  breaks  through.     This  is  called  the 


GERMINATION  AND  GROWTH 


45 


"  peg  "  ;  can  you  tell  its  use?  Could  the  cotyledons  get  out 
of  their  hard  covering  without  it?  Slip  the  peg  below  the 
coat  in  one  of  your  growing  specimens,  leave  it  in  the  soil, 
and  see  what  will  happen.  How  do  the  cotyledons  of  the 
squash  differ  from  those  of  the  bean  as  they  come  out  of  the 
seed  cover?  Do  they  act  as  foliage  leaves?  Do  you  see 
any  difference  in  the  development  of  the  plumule  in  the  two 
seeds  (Figs.  19,  25)  to  account  for  the  different  behavior  of 
the  cotyledons?  Sketch  three  seedlings  in  different  stages, 
labeling  correctly  the  parts  observed.  Make  a  similar  study 
of  the  castor  bean,  or  other  seedling  selected  by  your  teacher, 
and  illustrate  by  drawings. 

44.  Arched  and  straight  hypocotyls.  —  This  difference  in 
the  manner  of  getting  above  ground  is  an  important  one. 
That  by  means  of  the  arched  hypocotyl  is,  in  general,  charac- 
teristic of  the  process  of  germination  in  which  the  cotyledons 
come  above  ground,  while  the  straight  kind,  which  was  illus- 
trated in  the  corn  and  wheat,  is  the  prevail- 
ing method  when  the  cotyledons  remain 
below  ground.  Can  you  give  a  reason  for 
the  difference  ? 

45.  Polycotyledons ;  germination  of  the 
pine.  —  Examine  a  pine  seedling  just  begin- 
ning to  sprout.  What  part  emerges  first 
from  the  seed  coat?  Where  does  it  break 
through  ?  Where  did  3^ou  find  the  micropyle 
in  the  pine  seed?  (15.)  Can  you  give  a 
reason  why  the  hypocotyl  in  seeds  should 
break  through  the  coats  at  this  point  ?  How 
do  the  cotyledons  get  out  of  the  testa?  Is 
the  hypocotyl  arched  or  straight  in  germination?  How  does 
it  compare  with  the  bean  and  s(|uash  in  this  respect?  With 
the  corn  ?  Is  any  endosperm  left  in  the  testa  after  the  cotyle- 
dons have  come  out?  What  has  become  of  it?  Do  the 
cotyledons  function  as  leaves  ?  How  many  of  them  has  the 
specimen  you  are  studying  ?    Notice  the  little  knob  or  button 


60.  —  Pine 
scodliim  (Aftii-  ( iRAY). 


46  PRACTICAL  COURSE  IN  BOTANY 

at  the  upper  end  of  the  hypocotyl,  just  above  the  point  where 
the  cotyledons  are  attached;  this  is  the  epicotyl,  or  part 
above  the  cotyledons,  here  identical  with  the  plumule ;  does 
it  develop  as  rapidly  as  in  the  other  seedlings  you  have  ex- 
aniuiod  ? 

46.  Relation  of  parts  in  the  seedling.  —  Before  leaving  this 
subject,  it  is  imi)ortant  to  fix  clearly  in  mind  the  different 
parts  of  the  germinating  seedling  and  their  relation  to  both 
the  embryo  from  which  they  originated  and  the  plant  into 
which  they  are  to  develop.  The  part  labeled  ''  hypocotyl  " 
in  your  sketches  is  all  that  portion  of  the  embryo  below  the 
point  of  attachment  of  the  cotyledons.  In  germination  its 
upper  part  will  become  the  stem,  and  in  the  embryo  con- 
stitutes the  caulicle,  or  stemlet,  while  its  lower  part,  from 
which  the  root  will  develop,  is  the  radicle,  or  rootlet;  hence 
the  term  "  hypocotyl  "  includes  both  the  future  root  and 
stem.  The  plumule  is  that  part  of  the  embryo  between  the 
cotyledons  and  above  their  point  of  attachment  to  the  caulicle. 
It  is  the  upward  growing  point  of  the  young  plant,  and  hence 
the  place  of  attachment  of  the  cotyledon  is  the  first  node,  or 
point  of  leaf  origin,  on  the  stem. 

The  epicotyl,  in  contradistinction  to  the  hypocotyl,  is  all 
that  part  of  the  plant  above  the  insertion  of  the  cotyledons. 
Before  germination  it  is  identical  with  the  plumule.  As  the 
seedling  grows,  the  epicotyl  advances  its  growing  point  by 
adding  new  nodes  and  internodes,  as  the  spaces  between  the 
successive  points  of  leaf  insertion  are  called. 

47.  Botanical  terms.  —  As  the  prefixes  hypo  and  e-pi  are 
of  frequent  occurrence  in  botanical  works,  it  will  aid  in 
understanding  their  various  compounds  if  you  will  remem- 
ber that  hypo  always  refers  to  something  below  or  beneath, 
and  epi,  to  something  over  or  above.  With  this  idea  in  mind 
you  will  see  that  botanical  terms  are  a  labor-saving  device, 
since  it  is  much  easier,  in  making  notes,  to  use  a  single  de- 
scriptive word  than  to  write  out  the  long  English  equivalent, 
such  as  "  the  part  under  (or  over)  the  cotyledons." 


GERMINATION   AND  GROWTH 


47 


Practical  Questions 

1.  Do  the  cotyledons,  as  a  general  thing,  resemble  the  mature  leaves  of 
the  same  plants  ? 

2.  Name  some  plants  in  which  you  have  observed  differences,  and  ac- 
count for  them;  could  convenience  of  packing  in  the  seed  coats,  for  in- 
stance, or  of  getting  out  of  them,  have  any  bearing  on  the  matter  ? 

3.  Does  the  position  in  which  seeds  are  planted  in  the  ground  have 
anything  to  do  with  the  position  of  the  seedlings  as  they  appear  above  the 
surface  ? 

4.  Is  this  fact  of  any  importance  to  the  farmer  ? 

5.  Will  grain  that  has  begun  to  germinate  make  good  meal  or  flour? 
Why?     (27,36;  Exp.  25.) 


IV.     GROWTH 


some  lily  or  hyacinth  bulbs : 
well- 


Material.  —  Two  young  potted  plants 
seedlings  of  different  kinds,  —  some  with 
developed  taproots,  —  apple,  cotton,  and  maple 
are  good  examples. 

Appliances.  —  A  small  flat  dish,  some  mer- 
cury, and  a  piece  of  cork. 

Experiment  34.  How  does  the  root  in- 
crease IN  LENGTH  ?  —  Mark  off  the  root  of  a  very 
young  corn  seedling  into  sections  by  moistening  a 
piece  of  sewing  thread  with  indelible  ink  and 
applying  it  to  the  surface  of  the  root  at  intervals 
of  about  two  millimeters  (xo  of  an  inch),  or  by 
tying  a  thread  lightly  around  it  at  the  same  inter- 
vals. Lay  the  seedling  on  a  moist  bedding  be- 
tween two  panes  of  glass  kept  apart  by  a  sliver  of 
wood  to  prevent  their  injuring  the  root  by  pressure. 
Watch  for  a  day  or  two,  and  .you  will  see  that 
growth  takes  place  from  a  point  just  back  of  the 
tip  (Figs.  61,  62). 

Mark  off  a  seedling  of  the  bean  in  the  same 
way  and  watch  to  see  whether  it  increases  in  the  same  maimer  as  the  corn. 

Experiment  35.  How  does  the  stem  l\ckease  in  length?  —  Mark 
off  a  poi-tion  of  the  stem  of  a  bean  seedling  as  cxplaincHl  in  the  last  experi- 
ment, and  find  out  how  it  grows.  Allow  a  seedling  to  develop  until  it 
has  put  forth  several  leaves  and  measure  daily  the  spaces  between  them. 
Label  these  spaces  in  your  drawings,  "  internodes,"  and  the  points  where  the 
leaves  are  attached,  "  nodes."     Does  an  internode  stop  growing  when  the 


Figs.  61,  62.  — Seed- 
ling of  corn,  marked  to 
show  region  of  growth  : 
61,  early  stage  of  germi- 
nation ;  62,  later  stage. 


48 


PRACTICAL  COURSE   IN  BOTANY 


one  next  above  it  has  formed  ?  When  is  growth  most  rapid  ?  Reverse  the 
position  of  a  number  of  scedhngs  that  have  just  begun  to  sprout  and  watch 
what  will  happen.    After  a  few  days  reverse  again  and  note  the  effect. 


P 

63  64 

Figs.  63, 64. — Root  of  bean  seed- 
ling, measured  to  show  region  of 
growth  :  63,  early  stage  of 
tion  ;  64,  later  stage. 


Figs.  65,  66.  —  Stem  of  bean  seedling, 
measured  to  show  region  of  growth :  65, 
early  stage  of  growth  ;  66,  later  stage. 


E5CPERIMENT   36. 


67 
Figs.  67, 68. — Experiment  show- 
ing the  direction  of  growth  in  stems  : 
67,  young  potato  planted  in  an  in- 
verted position  ;  68,  the  same  after 
§n  ipterval  of  eight  days. 


Can  plants  grow  and  lose  weight  at  the  same 
TIME  ?  —  Remove  the  scales  from  a  white 
lilj^  bulb,  weigh  them,  and  lay  in  a  waiTn, 
but  not  too  damp  place,  away  from  the 
light.  After  a  time  bulblets  will  form  at 
the  bases  of  the  scales.  Weigh  them  again, 
and  if  there  has  been  any  loss,  account 
for  it.  The  experiment  may  be  tried  by 
allowing  a  potato  tuber  or  a  hyacinth  bulb 
to  germinate  without  absorbing  moisture 
enough  to  affect  its  weight. 

Experiment  37.  Is  the  direction  of 

GROWTH  A  MATTER  OP  ANY  IMPORTANCE  ? 

—  Plant  in  a  pot  suspended  as  shown  in 
Fig.  67,  a  healthy  seedling  of  some  kind, 
two  or  three  inches  high,  so  that  the 
plumule  shall  point  downward  through 
the  drain  hole  and  the  root  upward  into 
the  spjl.     Watch  the  action  of  the  stem 


GERMINATION  AND  GROWTH  49 

for  six  or  eight  days,  and  sketch  it  at  successive  intervals.  After  the  stem 
has  directed  itself  well  upward,  invert  the  pot  again,  and  watch  the  growth. 
After  a  week  remove  the  plant  and  notice  the  direction  of  the  root.  Sketch 
it  entire,  showing  the  changes  in  direction  of  growth. 

At  the  same  time  that  this  experiment  is  arranged,  lay  another  pot  with  a 
rapidly  growing  plant  on  one  side,  and  every  forty-eight  hours  reverse  the 
position  of  the  pot,  laying  it  on  the  opposite  side.  At  the  end  of  ten  or 
twelve  days  remove  the  plant  and  examine.  How  has  the  growth  of  root 
and  stem  been  affected  ? 

What  do  we  learn  from  these  experiments  and  from  Exp.  35  as  to  the 
normal  direction  of  growth  in  these  two  organs  respectively?  Can  you 
think  of  any  natural  force  that  might  influence  this  direction  ? 

Experiment  38.  To  show  that  plants  will  exert  force  rather 
THAN  CHANGE  THEIR  DIRECTION  OF  GROWTH.  —  Pin  a  sproutcd  bean  to  a 
cork  and  fasten  the  cork  to  the  side  of  a  flat  dish, 
as  shown  in  Fig.  69.  Cover  the  bottom  of  the  dish 
with  mercury  at  least  half  an  inch  deep,  and  over 
the  mercury  pour  a  layer  of  water.  Cover  the 
whole  with  a  pane  of  glass  to  keep  the  moisture  in,        ^ 

,,  »  ,    ,  m,  Ml  f  •  Fi"^'-  ^■^- — Lxpenment 

and  leave  tor  several  days.     Ihe  root  will  force  its  showing  the  ruot  of  a  seed- 
way  downward  into  the  mercury,  although  the  ling  forcing  its  way  down- 
latter  is  fourteen  times  heavier  than  an  equal  ward  through  mercury, 
bulk  of  the  bean  root  substance,  and  the  root  must  thus  overcome  a 
resistance  equal  to  at  least  fourteen  times  its  own  weight. 

48.  What  growth  is.  —  With  the  seedhng  begins  the 
growth  of  the  plant.  Most  people  understand  by  this 
word  mere  increase  in  size ;  but  growth  is  something  more 
than  this.  It  involves  a  change  of  form,  usually,  but  not 
necessarily,  accompanied  by  increase  in  bulk.  Mere  me- 
chanical change  is  not  growth,  as  when  we  bend  or  stretch 
an  organ  by  force,  though  if  it  can  be  kept  in  the  altered 
position  till  such  position  becomes  permanent,  or  as  we  say 
in  common  speech,  "  till  it  grows  that  way,"  the  change 
may  become  growth.  To  constitute  true  growth,  the  change 
of  form  must  be  permanent,  and  brought  about,  or  main- 
tained, by  forces  within  the  plant  itself. 

49.  Conditions  of  growth.  —  The  internal  conditions  de- 
pend upon  the  organization  of  the  plant.  The  essential 
external  conditions  are  the  same  as  those  required  for  germi- 


50  PRACTICAL  COURSK   IN   BOTANY 

nation :  food  material,  water,  oxygen,  and  a  sufficient 
degree  of  warmth.  It  may  be  greatly  influenced  by  other 
circumstances,  such  as  light,  gravitation,  pressure,  and 
(probably)  electricity ;  but  the  four  first  named  are  the  essen- 
tial conditions  without  which  no  growth  is  possible. 

50.  Cycle  of  growth.  —  When  an  organ  becomes  rigid 
and  its  form  fixed,  there  is  no  further  growth,  but  only  nutri- 
tion and  repair,  —  processes  which  must  not  be  confounded 
with  it.  Every  plant  and  part  of  a  plant  has  its  period  of 
beginning,  maximum,  decline,  and  cessation  of  growth.  The 
cycle  may  extend  over  a  few  hours,  as  in  some  of  the  fungi,  or, 
in  the  case  of  large  trees,  over  thousands  of  years. 

51.  Geotropism.  —  The  general  tendency  of  the  growing 
axes  of  plants  to  take  an  upward  and  downward  course  as 
shown  in  Exp.  37  —  in  other  words,  to  point  to  and  from  the 
center  of  the  earth  —  is  called  geotropism.  It  is  positive  when 
the  growing  organs  point  downward,  as  most  primary  roots 
do ;  negative  when  they  point  upward,  as  in  most  primary 
stems ;  and  transverse,  or  lateral,  when  they  extend  horizon- 
tally, as  is  the  case  with  most  secondary  roots  and  branches. 

52.  Gravity  and  growth.  —  It  cannot  be  proved  directly 
that  geotropism  is  due  to  gravity,  because  it  is  not  possible 
to  remove  plants  from  its  influence  so  as  to  see  how  they 
would  behave  in  its  absence.  The  effect  of  gravity  may  be 
neutralized,  however,  by  arranging  a  number  of  sprouting 
seeds  on  the  vertical  disk  of  a  clinostat,  an  instrument 
fitted  with  a  clockwork  movement  by  means  of  which  they 
may  be  kept  revolving  steadily  for  several  days.  By  this 
constant  change  of  position  gravity  is  made  to  act  on  them 
in  all  directions  alike,  which  is  the  same  in  some  respects  as 
if  it  did  not  act  at  all.  If  the  disk  is  made  to  revolve 
rapidly,  the  growing  root  tips  turn  toward  the  axis  of  motion, 
without  showing  a  tendency  to  grow  downward.  We  may 
then  conclude  th;it  geotropism  is  a  reaction  to  gravity. 

53.  Geotropism  an  active  force.  —  It  must  be  noted, 
however,  that  the  force  here  alluded  to  is  not  the  mere  me- 


GERMINATION  AND  GROWTH 


51 


chanical  effect  of  gravity,  due  to  weight  of  parts,  as  when  the 
bough  of  a  fruit  tree  is  bent  under  the  load  of  its  crop,  but 
a  certain  stimulus  to  which  the  plant  reacts  by  a  spontaneous 
adjustment  of  its  growing  parts.  In  other  words,  geotro- 
pism  is  an  active,  not  a  passive  function,  and  the  plant  will 
overcome  considerable  resistance  in  response  to  it.  (Exp.  38). 
54.  Other  factors.  —  The  direction  of  growth  is  influ- 
enced by  many  other  factors,  such  as  light,  heat,  moisture, 


contact  with  other  bodies, 
electricity.  The  result  of  all 
endless  variety  in  the  forms 
organs  that  seems  to  defy 
Heat,  unless  excessive,  gen- 
growth  ;  contact  sometimes 
causing  the  stem  to  curve 
turbing  object,  and  sometimes 
the  stem  to  curve  toward  the 
by  growing  more  rapidly  on 


and  perhaps  by 
these  forces  is  an 
and  growth  of 
all  law. 

erally  stimulates 
stimulates  it, 
away  from  the  dis- 
retards  it,  causing 
object  of  contact 
the  opposite  side, 


Fig.  70.  —  A  piece  of  a  haulm  of  millet  that  has  been  laid  horizontally,  righting 
itself  tphrough  the  influence  of  negative  geotropism. 

as  in  the  stems  of  twining  vines.  Light  stimulates  nutrition, 
but  generally  retards  growth.  The  movements  of  plants 
toward  the  hght  are  effected  in  this  way ;  growth  being 
checked  on  that  side,  the  plant  bends  toward  the  light. 

Practical  Questions 

1.  Why  do  stems  of  corn,  wheat,  rye,  etc.,  straighten  themselves  after 
being  prostrated  by  the  wind  ?     (51,  54.) 

2.  Do  plants  grow  more  rapidly  in  the  daytime,  or  at  night?      (54.) 

3.  Reconcile  this  with  the  fact  that  green  plants  will  die  if  deprived 
of  light. 


52  PRACTICAL  COURSE   IN  BOTANY 

4.  Which  grows  more  rapidly,  a  young  shoot  or  an  old  one?     (31,  50.) 

5.  Which,  as  a  general  thing,  arc  the  more  rapid  growers,  annuals  or 
perennials?     Herbaceous  or  woody-stemmed  plants? 

6.  Name  some  of  the  most  rapid  growers  you  know. 

7.  Of  what  advantage  is  this  habit  to  them? 

8.  Why  do  roots  form  only  on  the  under  side  of  subterraneous  stems  ? 
(ol.) 

9.  Why  do  new  twigs  develop  most  freely  on  the  upper  side  of  hori- 
zontal branches  ?     (51.) 

Field  Work 

(1)  Notice  the  various  seedlings  met  with  in  your  walks  and  see  how 
many  you  can  recognize  by  their  resemblance  to  the  mature  plants.  Ac- 
count for  any  differences  you  may  observe  between  seedlings  and  older 
plants  of  the  same  species.  Observe  the  cotyledons  as  they  come  up  and 
their  manner  of  getting  out  of  the  ground,  and  notice  the  ways  in  which 
this  is  influenced  by  moisture,  light,  and  the  nature  of  the  soil.  Where 
the  cotyledons  do  not  appear,  dig  into  the  ground  and  find  out  the  reason. 
Notice  which  method  of  emergence  occurs  in  each  case,  the  arched,  or 
straight,  and  account  for  it.  Observe  particularly  the  behavior  of  seed- 
lings in  hard,  sunbaked  soil.  If  you  see  any  of  them  lifting  cakes  of  earth, 
compare  the  size  and  weight  of  the  cake  with  that  of  the  seed ;  if  there  is 
any  disparity,  what  does  this  imply  ?  What  is  the  force  called  which  the 
plant  exercises  in  hfting  the  weight?     (51.) 

(2)  Notice  if  there  are  any  seeds  germinating  successfully  on  top  of 
the  ground,  and  find  out  by  what  means  their  roots  get  into  the  soil. 
Observe  what  effect  sun  and  shade,  moisture  and  drought,  and  the  nature 
of  the  soil  have  on  the  process.  Find  out  whether  roots  exercise  force  in 
penetrating  the  soil ;  what  kinds  they  penetrate  most  readily,  and  what 
kinds,  if  any,  they  fail  to  penetrate  at  all.  Notice  whether  seedlings  with 
taproots,  like  the  turnip  and  castor  bean,  or  those  with  fibrous  roots,  like 
corn  and  wheat,  are  more  successful  in  working  their  way  downward. 

(3)  Look  for  tree  seedlings.  Explain  why  seedlings  of  fruit  trees  are  so 
much  more  widely  distributed  in  cultivated  districts,  and  so  much  easier 
to  find  than  those  of  forest  trees.  Where  do  the  latter  occur,  as  a  general 
thing?  Account  for  the  fact  that  seedling  trees  are  so  much  more  rare 
than  germinating  herbs,  and  why  trees  like  the  oak  and  chestnut  and 
black  walnut  propagate  so  much  more  slowly,  in  a  state  of  nature,  than 
the  pine,  cedar,  ash,  and  maple. 

(4)  Observe  the  direction  of  growth  in  plants  on  the  sides  of  gullies  and 
ravines,  and  tell  how  it  is  influenced  by  geotropism.  Notice  whether  there 
are  other  influenc^es  at  work;  for  instance,  light,  or  in  the  case  of  roots, 
the  attraction  of  moisture. 


CHAPTER   III.     THE   ROOT 


I.     OSMOSIS  AND   THE  ACTION   OF  THE   CELL 


Material.  —  For  experiments  in  osmosis  provide  fresh  and  boiled 
slices  of  red  beet,  a  fresh  egg,  a  piece  of  ox  bladder  or  some  parchment 
paper;  glass  tubing,  thread,  twine,  elastic  bands,  salt  and  sugar  solutions. 
A  common  medicine  dropper  with  the  small  end  cut  off  will  answer  instead 
of  tubing  for  making  an  artificial  cell ;  or  an  eggshell  maj^  be  used,  by 
blowing  out  the  contents  through  a  puncture  in  the  small  end,  and  care- 
fully chipping  away  a  portion  of  the  shell  at  the  big  end,  leaving  the  lining 
membrane  intact.  The  different  liquids  can  be  put  into  the  shell  and  the 
exposed  membrane  placed  in  contact  with  the  liquid 
in  the  glass,  by  fitting  over  the  latter  a  piece  of  card- 
board with  a  hole  in  the  center  large  enough  for  the 
exposed  surface  to  protrude  sufficiently  to  touch  the 
water. 

55.  Object  of  the  experiments.  —  In  or- 
der to  understand  clearly  the  action  of  roots 
in  absorbing  nutrients  from  the  soil,  it  will 
be  necessary  to  learn  something  about  the 
movement  of  liquids  through  the  cells,  upon 
which  the  physiological  processes  of  the 
plant  depend.  For  this  purpose  make  an 
artificial  cell  by  tying  a  piece  of  ox  bladder 
or  parchment  paper  tightly  over  one  end  of 
a  small  glass  tube,  as  shown  in  Fig.  71. 

Experiment  39.  How  does  absorption  take 
PLACE  IN  THE  CELL  ?  —  (a)  Put  some  Salt  water  in 
a  wineglass,  partly  fill  the  tube  of  the  artificial  cell 
with  fresh  water,  and  mark  on  the  outside  of  both 
vessels  the  height  at  which  the  contained  liquid  stands.  Set  the  tube 
in  the  glass  of  salt  water  and  wait  for  results,  having  first  tested  care- 
fully to  make  sure  that  there  are  no  leaks  in  the  membrane.  After  half 
an  hour,  notice  whether  there  is  any  increase  of  water  in  the  glass,  as 
indicated  by  the  mark.     If  so,  where  did  it  come  from  ?    Is  there  any  loss 

53 


Fig.  71.— Artificial 
cell. 


54  PRACTICAL  COURSE  IN  BOTANY 

of  water  in  the  tube  ?  What  has  become  of  it  ?  How  did  it  get  out  ? 
Taste  it  to  see  if  any  of  the  salt  water  has  got  in.  Which  is  the  heavier, 
salt  water,  or  fresh?  (If  you  do  not  know,  weigh  an  equal  quantity  of 
each.)  In  which  direction  did  the  principal  flow  take  place;  from  the 
heavier  to  the  lighter,  or  from  the  lighter  to  the  heavier  liquid  ? 

(&)  Put  a  sugar  or  salt  solution  in  the  tube,  and  clear,  fresh  water  in 
the  glass,  marking  the  height  in  each  as  before.  Does  the  liquid  rise  or 
fall  in  the  tube  ?  Does  any  of  it  escape  into  the  water  of  the  glass,  and  if 
so,  is  it  more  or  less  than  before?  Which  now  contains  the  denser  fluid, 
the  tube  or  the  glass  ?  What  principle  governs  the  course  of  the  liquid  ? 
Try  the  same  experiment  with  (c),  the  same  liquid  in  both  vessels,  and 
notice  whether  there  is  a  greater  flow  in  one  direction  than  the  other,  as 
Indicated  by  a  comparison  with  the  marks  on  the  outside,  (d)  Put  in 
the  tube  some  of  the  white  of  a  raw  egg,  insert  in  a  glass  of  pure  water,  and 
note  the  effect,  (e)  Reverse,  with  water  in  the  tube  and  white  of  egg 
in  the  glass.  Does  the  water  rise  in  the  tube  as  before  ?  Test  the  contents 
for  proteins ;  has  any  of  the  albumin  passed  through  the  membrane  into 
the  tube  ? 

Experiment  40.  To  test  the  behavior  of  living  and  dead  cells.  — 
Slice  a  fresh  piece  of  red  beet  into  a  vessel  of  water  and  of  a  boiled  one  into 
another  vessel  of  the  same  liquid  at  the  same  temperature.  What  differ- 
ence do  you  notice  ?  Can  you  think  of  any  reason  why  the  boiled  one  gives 
up  its  juices  and  the  other  one  does  not  ? 

56.  Osmosis.  —  The  passage  of  liquids  or  of  solids  in  so- 
lution through  membranes  is  known  as  osmosis.  Our  experi- 
ments have  shown  that  the  principles  governing  the  osmotic 
movement  are:  (1)  the  passage  of  water  from  the  thinner 
liquid  toward  the  denser  takes  place  more  rapidly  than  in 
the  opposite  direction;  (2)  the  rapidity  of  the  transfer  de- 
pends on  the  difference  in  density;  (3)  crystallizable  sub- 
stances in  solution,  like  sugar  and  salt,  osmose  readily; 
(4)  albuminous  or  gelatinous  substances,  such  as  the  white 
of  an  egg,  osmose  so  slowly  that  the  cell  wall  may  be  regarded 
as  practically  impermeable  to  them. 

57.  Osmosis  a  form  of  diffusion.  —  Osmosis  is  related  to 
diffusion  as  a  part  to  the  whole.  In  other  words,  it  is  a  name 
given  to  the  process  when  it  takes  place  through  a  mem- 
brane, whether  solid,  as  the  outer  wall  of  the  cell,  or  semi- 
fluid, as  the  inner  wall  of  living  protoplasm.     Diffusion  may 


THE   ROOT  55 

therefore  take  place  without  osmosis,  that  is,  in  the  absence 
of  a  membrane,  as,  for  example,  when  we  sweeten  our  tea  or 
coffee  by  allowing  sugar  to  diffuse  through  it.  Many  mem- 
branes offer  little  resistance  to  the  osmotic  movement  of 
crystallizable  substances.  Such  membranes  are  said  to  be 
permeable.  Membranes  which  are  not  permeable  to  the  dis- 
solved soUds,  are  called  semi-permeable,  since  they  allow  the 
diffusion  of  water  but  not  of  the  substances  in  solution. 
Living  protoplasm  is  of  this  class.  It  is  only  very  slightly 
permeable  to  many  substances  toward  which,  when  dead,  it 
acts  as  a  permeable  membrane. 

58.  Absorption  in  living  and  dead  cells.  —  There  is  one 
great  difference  between  the  action  of  the  artificial  cell  used 
in  the  foregoing  experiments  and  that  of  the  cells  of  which 
a  living  body  is  built  up.  The  living  cell  always  has  at  least 
two  membranes.  One  of  these,  the  cell  wall,  is  readily  per- 
meable, while  the  other,  the  protoplasm,  is  semi-permeable 
—  that  is,  substances  in  solution  usually  diffuse  more  or  less 
slowly,  while  water  diffuses  rapidly.  Hence  in  the  living  cell 
the  protoplasm  exercises  a  power  of  absorption  independent 
of  the  cell  wall,  sometimes  rejecting  substances  admitted  by 
the  latter,  sometimes  retaining  others  to  which  it  is  perme- 
able, as  shown  in  Exp.  40.  In  the  boiled  beet  the  protoplasm 
had  been  killed  and  the  red  coloring  matter  passed  through 
it  unhindered,  while  in  the  living  one  it  was  held  back 
by  the  protoplasmic  lining,  which  is  thus  seen  to  control  the 
absorptive  properties  of  the  cell. 

59.  Plasmolysis.  —  Cells  can  be  killed  or  injured  in  other 
ways  than  by  heat;  for  example,  by  cold,  by  poisons,  by 
starvation,  and  by  overfeeding  through  the  use  of  too  much 
fertilizer  or  too  rich  a  one.  In  this  last  case,  the  soil  water 
becomes  impregnated  with  soluble  matter  from  the  manure, 
which  may  render  it  denser  than  the  sap  in  the  roots.  AVhen 
this  happens,  it  will  cause  the  osmotic  flow  to  set  outward 
and  thus  deplete  the  cell  of  its  water;  whence  we  have 
the  paradox  that  a  cell,  or  even  a  whole  plant,  may  be  starved 


56 


PRACTICAL  COURSE  IN  BOTANY 


by  overfeeding.  This  action  of  osmosis  in  withdrawing 
the  contents  from  a  cell  is  termed  plasmolysis,  and  you  can 
easily  understand  how  very  important  a  knowledge  of  the 
principles  governing  it  is  to  the  farmer  in  determining  the 
application  of  fertilizers  to  his  crops. 

Dead  cells,  although  powerless  to  carry  on  the  life  processes 
of  a  plant,  have  nevertheless  important  uses  in  serving  the 
purposes  of  mechanical  support  and  also  to  some  extent  in 
assisting  in  the  work  of  absorption,  though  their  function 
here  is  a  purely  mechanical  one. 

60.  Selective  absorption.  —  Different  plants  through 
their  roots  absorb  different  substances  from  the  soil  water,  or 

the  same  substance 
in  varying  degrees. 
Hence,  one  kind  of 
crop  will  exhaust 
the  soil  of  certain 
minerals  while  leav- 
ing other  kinds  in- 
tact, or  very  little 
diminished;  and  vice 
versa,  another  kind 
will  take  up  abun- 
dantly what  its  pred- 
ecessor has  rejected. 
In  this  sense,  plants 
are  said  to  exercise  a 
selective  power  in 
the  absorption  of  nu- 
trients. The  expres- 
sion must  not  be  understood,  however,  as  implying  any  kind 
of  volitional  discrimination.  It  is  merely  a  short  and  con- 
venient way  of  saying  that  the  cells  of  different  plants  possess 
different  degrees  of  permeability  to  certain  substances,  some 
being  more  permeable  to  one  thing,  some  to  another.  But 
beyond  this  rejection  of  untransmissible  substances  there  is  no 


l;JI 

9 

ij 

S 

m 

1|^ 

^ 

Fk;.  72. — -Root  of  a  troc  enveloping  a  rock. 
The  large  syeamore,  wluj.se  ba.se  i.s  partly  concealed 
by  the  trumpet  creeper  on  the  left  of  the  picture, 
is  growing  in  very  hard,  stony  soil,  and  one  of 
its  main  roots  has  molded  itself  so  completely  to  the 
ledge  of  rock  protruding  on  the  right,  that  when  a 
portion  of  it  was  torn  away,  as  shown  where  the  light 
streak  ends  at  a,  the  impress  of  its  fibers  was  so 
strongly  marked  on  the  rock  as  to  give  the  latter  the 
appearance  of  a  petrified  root. 


THE   ROOT 


67 


active  power  of  discrimination,  any  substance  that  can  pass 
through  the  cell  wall  and  its  protoplasmic  lining  being  taken 
in,  whether  useful,  unnecessary,  or  even  harmful.  These  may, 
however,  be  got  rid  of  by  excretion,  as  the  superfluous  water 
taken  in  with  dissolved  minerals  is  exhaled  from  the  leaves ; 
or  if  incapable  of  passing  out  by  osmosis,  rendered  harmless 
and  retained  in  the 
form  of  the  curious 
"crystalloids"  found 
in  various  parts  of 
plants.  But  while 
the  kind  of  selection 
exercised  by  vegeta- 
ble cells  implies  no 
power  of  choice,  as  a 
matter  of  fact  those 
substances  most 
used  by  the  plant  in 
carrying  on  its  life 
processes  are  ab- 
sorbed in  much 
greater  quantities 
than  others,  being 
transferred  to  parts 
where  growth  or 
other  changes  in  the 
plant  tissues  are  go- 
ing on,  and  there 
used  up  in  the  work  of  nutrition,  or  excreted  in  part  as  waste 
products.  In  either  case  their  passage  from  cell  to  cell  will 
give  rise  to  a  continuous  osmotic  current  in  that  direction, 
and  the  absorption  of  new  matter  will  go  on  in  proportion  to 
the  amounts  used  up. 

6i.  Definition.  —  Tissue  is  a  word  used  to  denote  any 
animal  or  vegetable  substance  having  a  uniform  structure 
organized  to  perform  a  particular  office  or  function.     Thus, 


Fig.  73.  —  Roots  of  elm  and  sycamore  contending  for 
isession  of  the  soil  on  a  rocky  bluff  on  the  Potomac. 


58  PRACTICAL  COURSE  IN  BOTANY 

for  instance,  we  have  bony  tissue  and  muscular  tissue  in 
animals ;  that  is,  tissue  made  of  bone  substance  and  muscle 
substance  and  doing  the  work  of  bone  and  muscle  respec- 
tively. Likewise  in  plants,  we  have  strengthening  tissue 
made  up  of  hard,  thick-walled  cells,  serving  mainly  for  pur- 
poses of  mechanical  support,  and  vascular  tissue,  made  up  of 
conducting  vessels  for  conveying  sap  —  and  so  on,  for  every 
separate  function. 

Practical  Questions 

1.  Wh}'  do  raspberries  and  strawberries  have  a  flabby,  wilted  look  if 
sugar  has  been  put  on  them  too  long  before  they  are  served  ?     (7,  56.) 

2.  Where  has  the  juice  gone  ?  What  caused  it  to  go  out  of  the  berries  ? 
(56,  59.) 

3.  Is  a  knowledge  of  the  principles  governing  osmosis  of  any  practical 
use  to  the  housekeeper  ? 

4.  Why  cannot  roots  absorb  water  as  freely  in  winter  as  in  summer? 
(Suggestion  :  which  is  the  heavier,  cold  or  warm  water  ? ) 

5.  Why  does  fertilizing  too  heavily  sometimes  injure  a  crop?     (59.) 

6.  Do  you  see  any  apparent  contradiction  between  the  action  of  plas- 
molysis  and  the  selective  power  of  protoplasm  ?     Can  you  reconcile  it  ? 

7.  If  a  piece  of  beet  that  has  been  frozen  is  placed  in  water  it  will  be- 
have just  as  the  slice  of  boiled  beet  did  in  Exp.  40;  explain.     (58,  59.) 

II.  MINERAL  NUTRIMENTS  ABSORBED  BY  PLANTS 

Material.  —  A  dozen  or  two  each  of  different  kinds  of  seeds  and  grains. 
A  small  portion  from  a  growing  shoot  of  a  woody  and  a  herbaceous  land 
plant,  and  of  some  kind  of  succulent  water  or  marsh  plant,  such  as  arrow 
grass  iSagittaria),  water  plantain,  etc. 

Appliances.  —  A  pair  of  scales ;  a  lamp,  stove,  or  other  means  of  burn- 
ing away  the  perishable  parts  of  the  specimens  to  be  studied. 

Experiment  41.  —  Do  the  tissues  of  plants  contain  mineral 
MATTER  ?  —  Take  about  a  dozen  each  of  grains  and  seeds  of  different  kinds, 
weigh  each  kind  separately,  and  then  dry  them  at  a  high  temperature,  but 
not  high  enough  to  scorch  or  burn  them.  After  they  have  become  perfectly 
dry,  Aveigh  them  again.  What  proportion  of  the  different  seeds  was  water, 
as  indicated  by  their  loss  of  weight  in  drying? 

Burn  all  the  solid  part  that  remains,  and  then  weigh  the  ash.  What 
proportion  of  each  kind  of  seed  was  of  incombustible  material?  What 
proportion  of  the  solid  material  was  destroyed  by  combustion  ? 


THE   ROOT 


59 


Experiment  42.  —  Do  they  contain  different  kinds  and  quanti- 
ties OF  minerals  ?  —  Test  in  the  same  way  the  fresh,  active  parts  of  any 
kind  of  ordinary  land  plant  (sunflower,  hollyhock,  pea  vines,  (itc),  and 
of  some  kind  of  succulent  water  or  marsh  plant  (Sagittaria,  water  lily, 
fern).  Do  you  notice  any  difference  in  the  amount  of  water  given  off  and 
of  solid  matter  left  behind  ?  In  the  character  of  the  ashes  left  ?  Have 
you  observed  in  general  any  difference  between  the  ashes  of  different 
woods ;  as,  for  instance,  hickory,  pine,  oak  ?  Compare  with  the  residue 
left  in  Exp.  21 ;  would  you  judge  that  the  residual  substances  are  of  the 
same  composition  ? 

62.  Essential  constituents.  —  The  composition  of  the 
ash  of  any  particular  plant  will  depend  upon  two  things: 
the  absorbent  capacity  of  the  plant  itself 
and  the  nature  of  the  substances  con- 
tained in  the  soil  in  which  it  grows.  But 
chemical  analysis  has  shown  that  how- 
ever the  ashes  may  vary,  they  always 
contain  some  proportion  of  the  follow- 
ing substances :  potassium  (potash), 
calcium  (lime),  magnesium,  phosphorus, 
and  (in  green  plants)  iron.  These  ele- 
ments occur  in  all  plants,  and  if  any  one 
of  them  is  absent,  growth  becomes  ab- 
normal if  not  impossible. 

The  part  of  the  dried  substances  that 
was  burned  away  after  expelling  the 
water  consists,  in  all  plants,  mainly  of 
carbon,  hydrogen,  oxygen,  nitrogen,  and 
sulphur,  in  varying  proportions.  These 
five  rank  first  in  importance  among  the 
essential  elements  of  vegetable  life,  and 
without  them  the  plant  cell  itself,  the  physiological  unit  of 
vegetable  structure,  could  not  exist.  They  compose  the 
greater  part  of  the  substance  of  every  plant,  carbon  alone 
usually  forming  about  one  half  the  dry  weight.  Other  sub- 
stances may  be  present  in  varying  proportions,  but  the  two 
groups  named  above  are  found  in  all  plants  without  excep- 


4        2        13        5 

Fig.  74.  —  Water  cul- 
tures of  buckwheat,  show- 
ing effect  of  the  lack  of  the 
different    food    elements : 

1,  with  all  the  elements; 

2,  without  potassium  ;  3, 
with  soda  instead  of  pot- 
ash ;  4,  without  calcium  ; 
5,  without  nitrates  or  am- 
monia salts. 


CO 


PRACTTOAL  COURSE   IN   BOTANY 


tion,  and  so  we  may  conclude  that  (with  the  possible  addition 
of  chlorine)  they  form  the  indispensable  elements  of  plant 
food.  Carbon,  hydrogen,  oxygen,  nitrogen,  sulphur,  and 
phosphorus  compose  the  structure  of  which  the  plant  is  built. 
The  other  four  ingredients  do  not  enter  into  the  substance  as 
component  parts,  but  aid  in  the  chemical  processes  by  which 
the  life  functions  of  the  plant  are  carried  on,  and  are  none 
the  less  essential  elements  of  its  food.  Figure  74  shows  the 
difference  between  a  plant  grown  in  a  solution  where  all 
the  food  elements  are  present,  and  others  in  which  some  of 
them  are  lacking. 

63.  How  plants  obtain  their  food  material.  —  Plants 
obtain  their  supply  of  the  various  mineral  salts  from  solu- 
tions in  the  soil  water  which 
they  absorb  through  their 
roots.  With  a  few  doubtful 
exceptions,  they  cannot  as- 
similate their  food  unless  it 
is  in  a  liquid  or  gaseous  form. 
Of  the  gases,  carbon  dioxide, 
oxygen,  and  hydrogen  can 
be  freely  absorbed  from  the 
air,  or  from  water  with  va- 
rious substances  in  solution, 
but  most  plants  are  so  con- 
stituted that  they  cannot  absorb  free  nitrogen  from  the  air ; 
they  can  take  it  only  in  the  form  of  compounds  from  nitrates 
dissolved  in  the  soil,  and  hence  the  importance  of  ammonia 
and  other  nitrogenous  compounds  in  artificial  fertilizers. 
Some  of  the  pea  family,  however,  bear  on  their  roots  little 
tubers  formed  by  minute  organisms  called  bacteria,  which 
have  the  power  of  extracting  nitrogen  directly  from  the 
free  air  mingled  with  the  soil ;  and  hence  the  soil  in  which 
these  tuber-bearing  legumes  decay  is  enriched  with  niirogen 
in  a  form  ready  for  use. 


i. 


Fig.  75.  —  Roots  of  soy  bean  bearing 
tubercle-forming  bacteria. 


THE   ROOT 


61 


Practical  Questions 

1.  Could  any  normal  plant  grow  in  a  soil  from  which  nitrogen  was  lack- 
ing?    Potash?     Lime?     Phosphorus?     (62.) 

2.  Could  it  live  in  an  atmosphere  devoid  of  oxygen  ?     Nitrogen  ?     Car- 
bon dioxide?     (62.) 

3.  Why  are  cow  peas  or  other  legumes  planted  on  worn-out  soil  to  renew 
it?     (63.) 

4.  Is  the  same  kind  of  fertilizer  equally  good  for  all  kinds  of  soil  ?     For 
all  kinds  of  plants  ?     (60,  62.) 

5.  Why  does  too  much  watering  interfere  with  the  nourishment  of 
plants?     (Exps.  26,  27.) 

6.  Are  ashes  fit  for  fertilizers  after  being  leached  for  lye?     (62.) 

7.  Why  will  plants  die,  or  make  very  slow  growth,  in  pots,  unless  the 
soil  is  renewed  occasionally?     (60,  62.) 


III.     STRUCTURE   OF   THE   ROOT 

Material.  —  Taproot  of  a  young  woody  plant  not  over  one  or  two 
years  old ;  apple  and  cherry  shoots  make  good  specimens.  For  showing 
root  hairs,  seedUngs  of  radish,  turnip,  or  oat  are  good,  also  roots  of  wan- 
dering Jew  grown  in  water ;  for  the  rootcap,  corn,  sunflower,  squash. 

64.  Gross  anatomy  of  the  root.  —  Cut  a  cross  section  of 
any  woody  taproot,  about  halfway  between  the  tip  and  the 
ground  level,  examine  it  with  a  lens,  and  sketch.  Label 
the  dark  outer  covering,  epidermis,  the  soft  layer  just  within 
that,  cortex,  the  hard,  woody  axis 
that  you  find  in  the  center,  vas- 
cular cylinder,  and  the  fine  sil- 
very lines  that  radiate  from  the 
center  to  the  cortex,  medullary 
rays  (in  a  very  young  root  these 
will  not  appear) .  Cut  a  section 
through  a  root  that  has  stood  in 
coloring  fluid  for  about  three 
hours  and  note  the  parts  colored 
by  the  fluid.  What  portion  of 
the  root,  would  you  judge  from 
this,  acts  as  a  conductor  of  the 
water  absorbed  from  the  ground? 


Fig.  76.  —  Cross  section  of  a  young 
taproot ;  a,  a,  root  hairs  ;  h,  epider- 
mis ;  c,  cortical  layer  ;  d,  fibrovascular 
cylinder.  Note  the  absence  of  med- 
ullary rays  during  the  first  year  0/ 
growth. 


62 


PRACTICAL  COURSE  IN  BOTANY 


Make  a  longitudinal  section  passing  through  the  central 
portion  of  the  root  and  extending  an  inch  or  two  into  the 
lower  part  of  the  stem.  Do  you  find  any  sharp  line  of  divi- 
sion between  them?  Notice  the  hard,  woody  axis  that  runs 
through  the  center.  This  is  the  vascular  cylinder  and  con- 
tains the  conducting  vessels,  the  cut  ends  of  which  were 
shown  in  cross  section  in  Fig.  76. 

65.  Distinctions  between  root  and  stem.  —  Pull  off  a 
branch  from  the  stem  and  one  from  the  root ;   which  comes 

off  the  more  easily  ?  Examine  the  points  of 
I  attachment  of  the  two  and  see  why  this  is  so. 

c^^l^^  This  mode  of  branching  from  the  central 
axis  instead  of  from  the  external  layers,  as 
in  the  stem,  is  one  marked  distinction  be- 
tween the  structure  of  the  two  organs.  In 
stems,  moreover,  branches  occur  normally 
above  the  points  of  leaf  insertion  at  the 
nodes  (46),  while  in  the  root  they  tend  to 
arrange  themselves  in  straight  vertical  rows. 
The  shoots  and  cions  that  often  originate 
from  them  are  not  normal  root  branches, 

but  outgrowths  from  irregular  or  adventitious  buds,  that 

may  occur  on  any  part  of  a  plant.     The  root  is  not  divided 

into   nodes   like   the   stem, 

and  never  bears  leaves. 

66.  The  active  part  of 
the  root.  —  It  is  only  the 
newest  and  most  delicate 
parts  of  the  root  that  pro- 
duce hairs  and  are  engaged 
in  the  active  work  of  absorp- 
tion, the  older  parts  acting 
mainly  as  carriers.  Hence, 
old  roots  lose  much  of  their 
characteristic  structure  and 

.    •■  1  c  i'  i^^-  ~^-  —  Root  ol  a  tree  on  the  side  of 

take  on  more  and  more  of     a  guUey,  acting  as  etem. 


Fig.  77.  — Verti- 
section  of  branching 
root,  showing  the 
branches,  n,  n,  origi- 
nating in  the  central 
axis,  /,  and  passing 
through  the    cortex, 


k 


THE   ROOT 


the  office  of  the  stem,  until  there  is  practically  no  difference 
between  them.  On  the  sides  of  gullies,  where  the  earth 
has  been  washed  from  around  the  trees,  we  often  see  the 
upper  portion  of  the  root  covered  with  a  thick  bark  and  ful- 
filling every  office  of  a  true  stem. 

67.  Minute  structure  of  the  root.  —  (a)  Mount  in  water 
and  place  under  the  microscope  a  portion  of  the  root  of  an 
oat  or  radish  seedling  containing  a  number  of  hairs.  In 
studying  the  thin,  transparent  roots  of  very  young  seedlings 
a  section  will  not  be  necessary.  Observe  whether  the  hairs 
originate  from  the  epidermis  or 
from  the  interior.  Are  they  true 
roots,  or  mere  outgrowths  from 
the  cells  of  the  epidermis?  Do 
they  consist  of  a  single  cell  or  a 
number  of  cells  each?  Notice 
what  very  thin  cell  walls  the 
hairs  have ;  is  there  any  advan- 
tage in  this  ?  The  interior,  trans- 
parent portion  of  the  hair  con- 
tains the  sap,  and  the  protoplasm 
forms  a  thin  lining  on  the  inner 
surface  of  the  wall ;  why  not 
the  sap  next  the  wall  and  the 
protoplasm  in  the  interior  ?  (58, 
60.) 

(6)  Next  examine  a  portion  «°^^  ^^^"^  *^«  extremity  of  the  cap. 
of  the  body  of  the  root  and  try  to  make  out  the  parts  as 
shown  in  Fig.  79,  and  compare  them  with  your  observa- 
tions in  64.  The  light  line  running  through  the  middle  is 
the  central  cylinder,  up  which  the  water  passes,  as  was  shown 
by  the  colored  liquid  in  64.  Outside  this  is  a  darker  por- 
tion (a.  Fig.  79),  corresponding  to  the  cortex  (rr,  Fig.  77). 
Besides  other  uses,  the  cortex  serves  to  prevent  the  loss 
of  water  as  it  passes  up  to  the  stem,  and  also,  in  fleshy 
roots  like  the  carrot  and  turnip,  for  the  storage  of  nourish- 


Fig.  79.  —  Longitudinal  section 
through  the  tip  of  a  young  root,  some- 
what diagrammatic  :  h,  h,  root  hairs  ; 
ep,  epidermis;  a,  cortex;  b,  central 
cylinder;  e,  sheath  of  the  eyhnder 
(endodermis) ;  g,  growing  point ;  c, 
root  cap ;  d,  dead  and  dying  cells  loos- 


64 


PRACTICAL  COURSE  IN  BOTANY 


inent.  Its  innermost  row  of  cells  is  thickened  into  the 
sheath,  or  endodermis  (e),  which  serves  as  an  additional 
protection  to  the  conducting  tissues.  The  extreme  outer 
layer,  from  the  cells  of  which  the  root  hairs  are  developed, 
is,  as  already  stated,  the  epidermis,  and  in  the  older  and 
more  exposed  parts  of  perennial  roots  is  displaced  by  the 
bark,  which  becomes  indistinguishable  from  that  of  the 
stem.     (66.) 

(c)  Look  at  the  tip  of  the  root  for  a  loose  structure  (c) 
fitting  over  it  like  a  thimble.  This  is  the  rootcap.  Do  you 
see  any  loose  cells  that  seem  to  have  broken  away  from  it  ? 
These  are  old  cells  that  have  been  pushed  to  the  front  by 
the  formation  of  new  growth  back  of  them,  and,  being  of  no 
further  use,  are  rubbed  off  by  friction  as  the  root  bores  its 
way  through  the  soil.  Draw  a  longitudinal  section  of  the 
root  as  it  appears  under  the  microscope,  labeling  all  the  parts. 
If  they  cannot  be  made  out  distinctly  in  the  specimen  exam- 
ined, use  sections  of  young  corn  or  bean  roots,  which  are 
larger  and  show  the  parts  more  distinctly. 

(d)  Place  under  the  microscope  a  thin  cross  section 
through  the  hairy  portion  of  a  primary  root  of  a  bean  or  pea 

seedling,  and  try  to  make 
out  the  parts  noted  above 
and  shown  in  cross  section  in 
Fig.  80.  Make  a  sketch  of 
what  you  see,  labeling  all 
the  parts  you  can  recognize. 
Show  in  your  drawing  the 
differences  in  the  size  and 
shape  of  the  cells  composing 
the  different  tissues.  No- 
tice in  the  central  cylinder 
(Fig.  80)  several  groups  of 
what  look  in  the  section  like 
little  round  pits,  or  holes,  sp.  These  are  the  cut  ends  of 
large-sized  tubes  or  ducts  that  convey  the  water  absorbed 


Fig.  80.  —  Cross  section  of  a  young  root, 
magnified  :  h,  hairs  ;  a,  cortex  ;  6,  central 
cylinder  ;  e,  sheath  or  endodermis  ;  ep,  epi- 
dermis; sp,  cut  ends  of  the  duets. 


I 


THE   ROOT  65 

by  tlie  roots  to  the  stem.  Each  set  of  these  tubes,  together 
with  a  number  of  smaller  ones  belonging  to  the  same  group, 
constitutes  a  fibrovascular  bundle  —  a  very  important  ele- 
ment in  the  structure  of  all  roots  and  stems,  as  these  bundles 
make  up  the  conducting  system  of  the  plant  body. 

IV.    THE   WORK   OF   ROOTS 

Material.  —  Germinating  seedlings  of  radish,  bean,  corn,  etc.;  a 
potted  plant  of  calla,  fuchsia,  tropseolum,  touch-me-not  (Impatiens),  or 
corn;  a  plant  that  has  been  growing  for  some  time  in  a  porous  earthen 
jar. 

Appliances.  —  Glass  tumblers ;  coloring  fluid  ;  wax  ;  some  coarse  net- 
ting; dark  wrapping  paper,  or  a  long  cardboard  box;  a  sheet  of  oiled 
paper ;  some  half-inch  glass  tubing ;  a  few  inches  of  rubber  tubing ;  an 
ounce  of  mercury ;  some  blue  litmus  paper ;  a  flower  pot  full  of  earth ; 
a  few  handfuls  of  sand,  clay,  and  vegetable  mold ;  a  pair  of  scales ;  a 
half  dozen  straight  lamp  chimneys,  or  long-necked  bottles  from  which 
the  bottoms  have  been  removed  as  directed  in  Exp.  53. 

Experiment  43.  Use  of  the  epidermis.  —  Cut  away  the  lower  end 
of  a  taproot;  seal  the  cut  surface  with  wax  so  as  to  make  it  perfectly 
water-tight,  and  insert  it  in  red  ink  for  at  least  half  the  remaining  length, 
taking  care  that  there  is  no  break  in  the  epidermis.  Cut  an  inch  or  two 
from  the  tip  of  the  lower  piece,  or  if  material  is  abundant,  from  another 
root  of  the  same  kind,  and  without  sealing  the  cut  surface,  insert  it  in  red 
ink,  beside  the  other.  At  the  end  of  three  or  four  hours,  examine  longitu- 
dinal sections  of  both  pieces.  Has  the  liquid  been  absorbed  equally  by 
both  ?  If  not,  in  which  has  it  been  absorbed  the  more  freely  ?  What  con- 
clusion would  you  draw  from  this,  as  to  the  passage  of  liquids  through 
the  epidermis? 

From  this  experiment  we  see  that  the  epidermis,  besides  protecting  the 
more  delicate  parts  within  from  mechanical  injury  by  hard  substances 
contained  in  the  soil,  serves  by  its  comparative  imperviousness  to  prevent 
evaporation,  or  the  escape  of  the  sap  by  osmosis  as  it  flows  from  the  root 
hairs  up  to  the  stem  and  leaves. 

Experiment  44.  To  show  that  roots  absorb  moisture.  —  Fill  two 
pots  with  damp  earth,  put  a  healthy  plant  in  one,  and  set  them  side  by 
side  in  the  shade.  After  a  few  days  examine  by  digging  into  the  soil  with 
a  fork  and  see  in  whicli  pot  it  is  drier.  Where  has  the  moisture  gone  ? 
How  did  it  get  out  ? 


on  PRACTICAL  COURSE  IN  BOTANY 

Experiment  45.  To  show  that  roots  shun  the  light.  —  Cover  the 
top  of  a  glass  of  water  with  thin  netting,  and  lay  on  it  sprouting  mustard 
or  other  convenient  seed.  Allow  the  roots  to  pass  through  the  netting  into 
the  water,  noting  the  position  of  root  and  stem.  Envelop  the  sides  of 
the  glass  in  heavy  wrapping  paper,  admitting  a  little  ray  of  light  through 
a  slit  in  one  side,  and  after  a  few  days  again  observe  the  relative  position 
of  the  two  organs.     How  is  each  affected  by  the  light? 

Experiment  46.  To  find  out  whether  roots  need  air.  -  Remove 
a  plant  from  a  porous  earthenware  pot  in  which  it  has  been  growing  for 
some  time ;  the  roots  will  be  found  spread  out  in  contact  with  the  walls 
of  the  pot  instead  of  embedded  in  the  soil  at  the  center.     Why  is  this  ? 

Experiment  47.  To  show  that  roots  seek  water.  —  Stretch  some 
coarse  netting  covered  with  moist  batting  over  the  top  of  an  empty  tumbler. 
Lay  on  it  some  seedlings,  as  in  Exp.  45,  allowing  the  roots  to  pass  through  the 
meshes  of  the  netting.  Keep  the  batting  moist,  but  take  care  not  to  let 
any  of  the  water  run  into  the  vessel.  Observe  the  .position  of  the  roots 
at  intervals,  for  twelve  to  twenty-four  hours,  then  fill  the  glass  with  water 
to  within  10  millimeters  (a  half  inch,  nearly)  or  less  of  the  netting,  let 
the  batting  dry,  and  after  eight  or  ten  hours  again  observe  the  position 
of  the  roots.  What  would  you  infer  from  this  experiment  as  to  the  affin- 
ity of  roots  for  water  ? 

Experiment  48.  W^hat  becomes  of  the  water  absorbed  by  roots 
—  Cover  a  calla  lily,  young  cornstalk,  sunflower,  tropa^olum,  or  other 
succulent  herb  with  a  cap  of  oiled  paper  to  prevent  evaporation  from  the 
leaves,  set  the  pot  containing  it  in  a  pan  of  tepid  water,  and  keep  the  tem- 
perature unchanged.  After  a  few  hours  look  for  water  drops  on  the  leaves. 
Where  did  this  water  come  from  ?     How  did  it  get  up  into  the  leaves  ? 

Experiment  49.  To  show  the  force  of  root  pressure.  —  Cut  off 
the  stem  of  the  plant  6  or  8  centimeters  (3  or  4  inches)  from  th»  base. 
Slip  over  the  part  remaining  in  the  soil  a  bit  of  rubber  tubing  of  about; 
the  same  diameter  as  the  stem,  and  tie  tightly  just  below  the  cut.  Pour 
in  a  little  water  to  keep  the  stem  moist,  and  slip  in  above,  a  short  piece 
of  tightly  fitting  glass  tubing.  Watch  the  tube  for  several  days  and  note 
the  rise  of  water  in  it.  The  same  phenomenon  may  be  observed  in  the 
"  bleeding  "  of  rapidly  growing,  absorbent  young  shoots,  such  as  grape, 
sunflower,  gourd,  tobacco,  etc.,  if  cut  off  near  the  ground  in  spring  when 
the  earth  is  warm  and  moist.  By  means  of  an  arrangement  like  that  shown 
in  Fig.  81,  the  force  of  the  pressure  exerted  can  be  measured  by  the  dis- 
placement of  the  mercury.  This  flow  cannot  be  due  to  the  giving  off  of 
moisture  by  the  leaves,  since  they  have  been  removed.  Their  action, 
when  present,  by  causing  a  deficiency  of  moisture  in  certain  places  may 


THE  ROOT 


67 


influence  the  direction  and  rapidity  of  the 
current,  but  does  not  furnish  the  motive 
power,  which  evidently  comes,  in  part  at 
least,  from  the  roots,  and  is  the  expression 
of  their  absorbent  activity. 

Experiment  50.     To  show  that  roots 

CAUSE   THE    OCCURRENCE    OF   ACIDS.  —  Lay 

a  piece  of  blue  litmus  paper  on  a  board  or 
on  a  piece  of  glass  slightly  tilted  at  one  end 
to  secure  drainage.  Cover  the  surface  with 
an  inch  of  moist  sand  and  plant  in  it  a 
number  of  healthy  seedlings.  Acids  have 
the  property  of  changing  blue  litmus  to 
red;  hence,  if  you  find  any  red  stains  on 
the  paper  where  the  roots  have  penetrated, 
what  are  you  to  conclude  ? 

Carbon  dioxide  has  a  slight  acid  reac- 
tion and  is  caused  to  form  in  varying 
quantities  by  all  roots.  Probably  other 
substances,  and  these  not  a  few,  are  actu- 
ally excreted. 

Experiment  51.  Can  the  absorbent 
power  of  roots  be  interfered  with  ?  — 
Place  the  roots  of  a  number  of  seedlings 
with  well-developed  hairs  in  a  weak  solution  of  saltpeter  —  10  grams  (about 
I  of  an  ounce)  to  a  pint  of  water,  and  others  in  a  stronger  solution  —  say 
30  grams,  or  1  ounce,  to  a  pint.  Try  the  same  -experiment  with  weak 
and  strong  solutions  of  any  conveniently  obtainable  liquid  fertilizer. 
After  45  minutes  or  an  hour  examine  the  roots  under  a  lens  and  note  the 
change  that  has  taken  place.  What  has  gone  out  of  them  ?  What  caused 
the  loss  of  the  contained  sap  ? 

Experiment  52.  To  tbst  the  weight  of  soils.  —  Thoroughly  dry 
and  powder  a  pint  each  of  sand  and  clay,  measure  accurately,  and  balance 
against  each  other  in  a  pair  of  scales.  Which  weighs  more,  bulk  for  bulk, 
a  "light"  soil,  or  a  "heavy"  one?     (77.) 

Experiment  53.  To  test  the  capacity  of  soils  for  absorbing  and 
retaining  moisture.  —  Arrange,  as  shown  in  Fig.  82,  a  number  of  long- 
necked  bottles  from  which  the  bottom  has  been  removed.  This  can  be 
done  by  making  a  small  indentation  with  a  file  at  the  point  desired  and 
leading  the  break  round  the  circumference  with  the  end  of  a  glowing  wire 
or  a  red-hot  poker.    The  crack  will  follow  the  heated  object  with  sufficient 


Fig.  81. — Arrangement  for 
estimating  the  force  of  root  pres- 
sure :  s,  stub  of  the  cut  stem  ;  g, 
glass  tubing  joined  by  means  of 
the  rubber  tuijing,  t,  to  the  stem  ; 
m,  mercury  forced  up  the  glass 
tube  by  water,  w,  pumped  from 
the  soil  by  the  roots. 


68  PRACTICAL  COURSE   IN  BOTANY 

regularity  to  answer  the  purpose.  Tie  a  piece  of  thin  cloth  over  the  mouth 
of  each  bottle  and  invert  with  the  necks  extending  an  inch  or  two  into 
empty  tum!)lers  placed  beneath.  Fill  all  to  the  same  height  with  soils  of 
different  kinds  —  sand,  clay,  gravel,  loam,  vegetable  mold,  etc.  —  and  pour 


Fig.  82.  — Apparatus  for  testing  the  capacity  of  soils  to  take  in  and  retain 
moisture. 

over  each  the  same  quantity  of  water  from  above.  Watch  the  rate  at 
which  the  liquid  filters  through  into  the  tumblers.  Which  loses  its  mois- 
ture soonest  ?     Which  retains  it  longest  ? 

Next  leave  the  soils  in  the  bottles  dry,  fill  the  tumblers  up  to  the  necks 
of  the  bottles,  and  watch  the  rate  at  which  the  water  rises  in  the  different 
ones.  The  power  of  soils  to  absorb  moisture  is  called  capillarity.  Which 
of  your  samples  shows  the  highest  capillarity  ?  Which  the  lowest  ?  Do 
you  observe  any  relation  between  the  capillarity  of  a  soil  and  its  power  of 
retention  ? 

68.  Roots  as  holdfasts.  —  One  use  of  ordinary  roots  is 
to  serve  as  props  and  stays  for  anchoring  plants  to  the  soil. 
Tall  herbs  and  shrubs,  and  vegetation  generally  that  is 
exposed  to  much  stress  of  weather,  are  apt  to  have  large, 
strong  roots.  Even  plants  of  the  same  species  will  develop 
systems  of  very  different  strength  according  as  they  grow 
in  sheltered  or  exposed  places. 


THE   ROOT 


69 


Fig.  83.  —  Dandelion 
region  at  low  altitude  ;  b, 


a,  common  form,  grown  in  plains 
alpine  form. 


69.   Root  pull.  —  Roots  are  not  mere  passive  holdfasts, 
but  exert  an  active  downward  pull  upon  the  stem.     Notice 
the  rooting    end 
of  a  strawberry  or  ^  i  v' 

raspberry  shoot 
and  observe  how 
the  stem  appears 
to  be  drawn  into 
the  ground  at  the 
rooting  point. 
In  the  leaf  ro- 
settes of  herbs 
growing  flat  on 
the  ground  or  in 
the  crevices  of  walls  and  pavements,  the  strong  depression 
observable  at  the  center  is  due  to  root  pull.     (Fig.  84.) 

70.  Storage  of  food.  —  Another  of- 
fice of  roots  is  to  store  up  food  for  the 
use  of  the  plant.  This  is  done  chiefly 
in  the  tissues  of  fleshy  roots  and  tu- 
bers, and  gives  to  them  their  great 
economic  value.  Next  to  grains  and 
cereals,  roots  probably  furnish  a  larger 
portion  of  food  to  the  human  race 
than  any  other  crop.  In  addition  to 
this  they  are  also  the  source  of  valu- 
able drugs,  condiments,  and  dyes. 

71.  Absorption  and  conveyance  of 
sap.  —  But  the  most  important  func- 
tion of  roots  is  that  of  absorption. 
By  their  action  the  soil  water  and  the 
minerals  contained  in  it  are  drawn  up 
into  the  plant  body  and  made  avail- 
able for  conversion  by  the  leaves  into 

organic  foods,  as  will  he  explained  in  another  chapter.     From 
the  nature  of  their   function,  most  roots  have  naturally  a 


'ih'l 


ivo 


Fig.  84.  —  Raspberry  sto- 
lon showing  root  pull. 


70 


PRACTICAL  COURSE  IN  BOTANY 


strong  affinity  for  water,  and  its  presence  or  absence  has  a 
marked  influence  on  their  direction  of  growth,  being  often 
sufficient  to  overcome  that  of  geotropism  (Exp.  47).  There 
are  many  trees  and  shrubs,  notably  willow,  sweet  bay,  red 
birch,  and  the  like,  that  grow  best  on  the  banks  of  streams 
and  ponds,  where  their  roots  can  have  direct  access  to  water. 
Excess  of  moisture,  however,  is  injurious  to  most  land  plants 
by  preventing  the  roots  from  getting  sufficient  air  for  res- 
piration. 

72.  The  conditions  of  absorption.  —  The  sap  in  the  root 
cells  is  normally  denser  than  the  water  in  the  soil,  so  there  is 
a  continuous  flow  from  the  latter  to  the  former.  But  if, 
for  any  reason,  the  density  of  the  liquids  should  be  reversed, 
the  flow  would  set  in  the  opposite  direction,  and  if  continued 
long  enough,  the  strength  of  the  plant  would  be  literally 
"  sapped  "  by  the  exhaustion  of  its  tissues,  so  that  it  would 
die.     What  is  this  process  of  cell  exhaustion  called  ? 

73.  The  use  of  acid  secretions  to  the  root.  —  It  was 
shown  in  Exp.  50  that  carbon  dioxide  and  probably  other  sub- 
stances occur  in  the  im- 
mediate vicinity  of  roots. 
Carbon  dioxide  is  an  ac- 
tive agent  in  dissolving 
the  various  mineral  mat- 
ters contained  in  the  soil, 
and  as  these  last  can  be 
absorbed  only  in  a  liquid 
or  a  gaseous  state  (63), 
the  advantage  to  the 
root  as  an  absorbent  or- 
gan, of  being  able  to  se- 
crete such  active  sol- 
vents, is  obvious. 

74.   Relation  of  roots 
x^    OK       A     .     1      .  .  u-  to  the  soil.  —  In  order  to 

Fig.  85.  —  A  natural  root  etching, 

found  on  a  piece  of  slate.  perform  their  work  of  ab- 


THE  ROOT  71 

sorption,  roots  must  have  access  to  a  suitable  soil.  To  pro- 
duce  the  best  results  a  soil  must  contain  (1)  all  the  essential 
mineral  constituents  (62) ;  (2)  moisture  for  dissolving  these 
materials ;  and  (3)  air  enough  to  supply  the  oxygen  which  is 
necessary  to  the  life  processes  of  all  green  plants. 

75.  Composition  of  soils.  —  Sand,  clay,  and  humus,  or 
vegetable  mold,  with  the  various  substances  dissolved  in 
them,  constitute  the  basis  of  cultivated  soils.  A  mixture 
of  sand,  clay,  and  humus  is  called  loam.  When  the  propor- 
tion of  humus  is  very  large  and  well  decomposed,  the  mixture 
is  called  muck.  Pure  sand  contains  but  little  nourishing 
matter  and  is  too  porous  to  retain  water  well.  Pure  clay 
is  too  compact  to  be  easily  permeable  to  either  air  or  water. 
Most  soils  are  composed  of  a  mixture  of  the  two  with  vege- 
table mold  in  varying  proportions,  giving  a  sandy  loam,  or 
a  clay  loam,  as  the  case  may  be. 

76.  Tillage.  —  The  advantages  of  tillage  are:  (a)  that  by 
breaking  up  the  hard  lumps  it  renders  the  soil  more  per- 
meable to  air  and  water  and  more  easily  penetrable  by  the 
roots  in  their  search  for  food;  (6)  the  covering  of  loose, 
friable  earth  left  by  the  plow  and  the  harrow  acts  as  a  mulch, 
and  by  shading  the  soil  below,  prevents  too  rapid  a  loss  of 
water  by  evaporation.  Where  the  essential  food  ingredients 
are  present,  good  tillage  counts  for  more  in  making  a  crop 
than  the  original  quality  of  the  soil. 

77.  Light  and  heavy  soils.  —  These  terms  are  used  by 
farmers  not  in  relation  to  the  weight  of  soils,  but  in  reference 
to  the  ease  or  difficulty  with  which  they  are  worked.  Light 
soils  contain  a  preponderance  of  sand;  heavy  ones,  of  clay. 

Practical  Questions 

1.  Will  plants  grow  better  in  an  earthen  pot  or  a  wooden  box  than 
in  a  vessel  of  glass  or  metal?    Why?     (Exp.  46.) 

2.  Which  absorb  more  from  the  soil,  plants  with  light  roots  and  abun- 
dant foliage,  or  those  with  heavy  roots  and  scant  foliage  ?  (Suggestion* 
roots  absorb  fiom  the  soil ;  leaves,  mainly  from  the  air.) 


72  PRAC^TICAL   COURSE   IN   BOTANY 

3.  Why  arc  willows  so  generally  selected  for  planting  along  the 
borders  of  streams  in  order  to  protect  the  banks  from  washing?     (71.) 

4.  Why  are  the  conducting  tissues  of  roots  at  the  center  instead  of 
near  the  surface  as  in  stems?     (67,  6.) 

5.  Why  does  corn  never  grow  well  in  swampy  ground  ?    (74 ;  Exp.  46. ) 

6.  Why  are  fleshy  roots  so  much  larger  in  cultivated  plants  than  in 
wild  ones  of  the  same  species  ?     (74,  76.) 

7.  When  the  use  of  a  particular  kind  of  fertilizer  causes  the  leaves 
of  the  plants  to  which  it  has  been  applied  to  turn  brown,  so  that  the 
farmer  says  they  have  been  "  burned  "  by  it,  to  what  cause  is  the  trouble 
due?     (59,72.) 

8.  Why  do  farmers  speak  of  turnips  and  other  root  crops  as  "heavy 
feeders"?     (70,71.) 

9.  Which  is  more  exhausting  to  the  soil,  a  crop  of  beets,  or  one  of  oats  ? 
Onions,  or  green  peas?     (See  2,  suggestion.) 

10.  Why  will  inserting  the  end  of  a  wilted  twig  in  warm  water  some- 
times cause  it  to  revive?     (Exps.  48,  49.) 

V.    DIFFERENT   FORMS    OF   ROOTS 

Material.  —  Examples  of  taproots :  bean,  pea,  cotton,  maple  seedlings, 
or  any  kind  of  very  young  woody  root.  Fibrous  :  any  kind  of  grass  or 
grain.  Fleshy :  parsnip,  turnip,  carrot,  dahlia,  sweet  potato.  Water : 
duckweed,  pondweed,  or  a  cutting  of  wandering  Jew  grown  in  water. 
Parasitic  :  mistletoe,  dodder,  beech  drops.  Aerial  and  adventitious :  the 
aerial  roots  of  old  scuppernong  vines,  climbing  roots  of  ivy  and  trumpet 
vine,  prop  roots  from  the  lower  nodes  of  cornstalks  and  sugar  cane. 

78.  Basis  of  distinction.  —  Roots  vary  in  form  and  ex- 
ternal structure  according  to  their  origin,  function,  and 
surroundings.  In  reference  to  the  first,  they  are  classed 
as  primary  or  secondary ;  in  regard  to  the  second,  as  dry  or 
fleshy;  while  as  to  surroundings,  they  may  be  adapted  to 
either  the  soil,  water,  air,  or  the  parasitic  habit.  Soil  roots 
are  the  normal  form.  According  to  their  mode  of  growth 
they  are  either  fibrous  or  axial. 

79.  Taproots.  —  These  are  the  common  form  of  the  axial 
type.  Compare  the  root  of  any  young  hardwood  cion  a 
year  or  two  old  with  one  of  a  mature  stalk  of  corn  or 
other  grain,  and  with  the  roots  of  seedlings  of  the  same 
species.     Notice  the  difference  in  their  mode  of  growth.     In 


THE   ROOT 


73 


Plate  3.  —  Aerial  roots  of  a  Mexican  "  strangling  "  fig,  enveloping  the  trunk 
of  a  palm  {From  "  Rep't.  Mo.  Bot.  Garden"). 


74 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  86.  —  Brauchuu  tap 
root  of  maple. 


the  first  kind  a  single  stout  prolongation  called  a  taproot 
proceeds  from  the  lower  end  of  the  hypocotyl  and  continues 
the  axis  of  growth  straight  downward,  unless  turned  aside 
by  some  external  influence.  A  taproot  may  be  either  simple, 
as  in  the  turnip,  radish,  and  dandelion, 
or  branched,  as  in  most  shrubs  and 
trees.  In  the  latter  case  the  main  axis 
is  called  the  primary  root,  and  the 
branches  are  secondary  ones. 

80.  Fibrous  and  fascicled  roots. — 
Where  the  main  axis  fails  to  develop, 
as  in  the  corn  and  grasses  generally, 
a  number  of  independent  branches  take 
its  place,  forming  what  are  known  as 
fibrous  roots.  Both  fibrous  and  tap- 
roots may  be  either  hard  or  fleshy. 
The  turnip  and  carrot  are  examples  of 
fleshy  taproots,  the  dahha  and  rhubarb  of  fascicled  roots. 
The  function  of  both  is  the  storage  of  nourishment.  The 
sweet  potato  is  an  example  of  a  tuberous  root. 

81.  Practical  importance  of  this  distinction.  —  The  dif- 
ference between  axial  and  fibrous  roots  has  important  bear- 
ings in  agriculture.  The  first  kind, 
which  are  characteristic  of  most  dicot- 
yls,  strike  deep  and  draw  their  nour- 
ishment from  the  lower  strata  of  the 
soil,  while  the  fibrous  and  fascicled,  or 
radial  kinds,  as  we  may  call  them  for 
want  of  a  better  name,  spread  out  near 
the  surface  and  are  more  dependent  on 
external  conditions. 

82.  Roots  that  grow  above  ground.  —  The  kinds 
roots  that  have  just  been  considered  are  all  subterranean, 
and  bring  the  plant  into  relation  with  the  earth,  whether  for 
the  purpose  of  absorbing  nourishment,  or  of  mechanical  sup- 
port, or,  as  in  the  majority  of  cases,  for  both.     Many  plants, 


Fig.  87.  —  Fibrous  root. 


of 


THE  ROOT  75 

however,  do  not  get  their  mineral  nutrients  directly  from 
the  soil,  and  these  give  rise  to  various  forms  suited  to  other 
conditions  of  alimentation. 

83.  Adventitious  roots.  —  This  name  applies  to  any  kinds 
of  roots  that  occur  on  stems,  or  in  other  unusual  positions. 
They  may  be  considered  as  intermediate  between  the  two 
classes  named  in  81;  for  while  their  starting  point  is  above 
ground,  they  generally  end  by  fixing  themselves  in  the  soil, 
where  they  often  function  as  normal  roots.  Familiar  examples 
are  the  roots  that  put  out  from  the  lower  nodes  of  corn  and 
sugar  cane  stalks,  and  serve  both  to  supply  additional  mois- 
ture and  to  anchor  the  plant  more  firmly  to  the  soil.  Most 
plants  will  develop  adventitious  roots  if  covered  with  earth, 
or  even  if  merely  kept  in  contact  with  the  ground.  The 
gardener  takes  advantage  of  this  capacity  when  he  propa- 
gates by  cuttings  and  layers. 

84.  Water  roots.  — ■  These  are  generally  white  and  thread- 
like and  more  tender  and  succulent  than  ordinary  soil  roots, 
because  they  have  less  work  to  do.  Floating  and  immersed 
plants,  such  as  bladderwort  and  hornwort  {Cerato-phyllum) 
have  no  need  of  absorbent  roots,  since  the  greater  part  of 
their  surface  is  in  contact  with  water  and  can  absorb  directly 
what  is  needed. 

Land  plants  will  often  develop  water  roots  and  thrive 
for  a  time  if  the  liquid  holds  in  solution  a  sufficient  quantity 
of  air  and  mineral  nutrients.  Place  a  cutting  of  wandering 
Jew  in  a  glass  of  clear  water,  and  in  from  four  to  six  days  it 
will  develop  beautiful  water  roots  in  which  both  hairs  and 
cap  are  clearly  visible  to  the  naked  eye. 

85.  Haustoria,  from  a  Latin  word  meaning  to  drain, 
or  exhaust,  is  a  name  given  to  the  roots  of  parasitic  plants, 
or  such  as  live  by  attaching  themselves  to  some  other  living 
organism,  from  which  they  draw  their  nourishment  ready 
made.  Their  roots  are  adapted  to  penetrating  the  sub- 
stance of  the  host,  as  their  victim  is  called,  and  absorbing 
the  sap  from  it.     Dodder  and  mistletoe  are  the  best-known 


76 


PRArTTCAL  rOT'RSE   IN  BOTANY 


examples  of  plant  parasites,  though  the  latter  is  only  partially 
parasitic,  as  it  merely  takes  up  the  sap  from  the  host  and 

manufactures   its   own  food 


U 

A  B 

Fig.  88. — Beech  root:  A,  grown  in 
unsterilized  wood  humus :  p,  strands  of 
fungal  hypha;,  associated  at  a,  with 
humus ;  B,  grown  in  wood  humus  freed 
from  fungus  by  sterihzation  —  it  is  not 
provided  with  fungal  hyphse,  and  has 
root  hairs,  li.  (A  and  B  both  several 
times  magnified.) 


by  means  of  its  green  leaves. 
86.  Saprophytes.  —  Akin 
to  parasites  are  saprophytes, 
which  live  on  dead  and  decay- 
ing vegetable  matter.  They 
are  only  partially  parasitic 
and  do  not  bear  the  haustoria 
of  true  parasites.  Many  of 
them,  of  which  the  Indian 
pipe  (Monotropa)  and  coral 
root  are  familiar  examples, 
obtain  their  nourishment  in 
part,  at  least,  by  association  with  certain  saprophytic  fungi, 
which  enmesh  their  roots  in  a  growth  of  threadlike  fibers 
that  take  the  place  of  root  hairs  and  absorb  organic  food 
from  the  rich  humus  in 
w^hich  these  plants  grow. 
Such  growths  are  called 
mycorrJiiza,  meaning 
"  fungal  roots."  Similar 
associations  are  formed 
by  some  of  the  higher 
plants  also.  The  root- 
lets of  the  common  beech 
and  of  certain  of  the 
pine  family,  for  instance, 
are  often  enveloped  in 
a  network  of  fungus  fi- 
bers, and  in  this  case  root  Fi<-  89.  —An  air  plant  (Tillandsia),  growing 
1      •                  111                   on  the  underside  of  a  bough. 

hairs  are  developed  very 

poorly,  or  not  at  all.  Besides  greatly  increasing  the  absorbent 
surface  by  their  ramification  through  the  soil,  the  mycorrhizal 
threads  may  possibly  benefit  the  plant  in  other  ways  also,  as. 


i 

^ 

^s" 

m 

\ 

THE   ROOT 


77 


for  instance,  by  bringing 
about  chemical  changes 
that  might  aid  in  the 
work  of  nutrition. 

87.  Epiphytes,  or  air 
plants.  —  In  the  proper 
meaning  of  the  word 
these  are  not  parasitic, 
but  use  their  host  merely 
as  a  mechanical  support 
to  bring  them  into  better 
light  relations.  The 
name,  however,  is  loosely 
applied  to  all  plants  that 
find  a  lodgment  on  the 
trunks  and  branches  of 
trees,  whether  parasites 
or  true  epiphytes  that 
draw  no  nourishment 
from  the  host.  Not  in- 
frequently the  latter  is 
killed  by  them  through 
suffocation,  overweight- 
ing, or  the  constriction 
of  the  stems  by  close 
clinging  twiners. 

88.  Aerial  roots  are 
such  as  have  no  connec- 
tion at  all  with  the  soil  or 
with  any  host  plant,  ex- 
cept as  they  may  lodge 
upon  the  trunks  and 
branches  of  trees  for  a 
support.  In  other  than 
purely  epiphytic  plants, 
which  get  all  their  nour- 


Fk;.  90. — A  single  strand  of  TiUandsia 
nxncoiden,  a  rootless  epiphyte  belonging  to  the 
pineapple  family  ;  better  known  as  the  "  Span- 
ish moss"  that  drapes  the  boughs  of  trees  so 
conspicuously  in  the  warm  parts  of  America. 
Two-thirds  natural  size.  (Photographed  by  C. 
F.  O'Keefe.) 


78  PRACTICAL  COURSE  IN  BOTANY 

ishment  from  the  air,  they  are  generally  subsidiary  to  soil 
roots,  like  the  long  dangling  cords  that  hang  from  some 
species  of  old  grapevines ;  or  they  subserve  other  purposes 
altogether  than  absorbing  nourishment,  as  the  climbing 
roots  of  the  trumpet  vine  and  poison  ivy.  A  very  remark- 
able development  of  aerial  roots  takes  place  in  the  "stran- 
gling fig  "  of  Mexico  and  Florida,  which  begins  life  as  a  small 
epiphyte,  from  seeds  dropped  by  birds  on  the  boughs  or 
trunks  of  trees.  When  it  gets  well  started,  the  young  plant 
sends  down  enormous  aerial  roots,  which  find  their  way  to 
the  ground,  and  in  time  so  completely  envelop  the  host  that 
it  is  literally  strangled  to  death  (Plate  3,  p.  73).  When  this 
support  is  removed,  the  sheathing  roots  take  its  place  and 

t  become   to    all    intents 
and  purposes  the  stem 
^  of  the  fig  tree,   which 


_^  .    .  '^-'^"^6^^  -^X.^-^  ^  now  leads  an  independ- 


Sf  V^7h?C^"^^  ^9-   The  root  system. 

—  The  entire  mass  of 
roots  belonging  to  a 
plant,  with  all  its  rami- 
fications   and    subdivi- 

FiG.  91.  —  Root  system  of  a  tobacco  plant.        gions,    COmpOSCS    a    rOOt 

system.  The  extent  of  root  expansion  is  in  general  about 
equal  to  that  of  the  crown,  thus  bringing  the  new  and 
active  parts  under  the  drip  of  the  boughs  where  the  moisture 
is  most  abundant.  Some  plants  have  root  systems  out  of 
all  seeming  proportion  to  their  size.  A  catalpa  seedling 
six  months  old  showed,  by  actual  measurement,  250  feet 
of  root  growth,  and  it  is  estimated  that  the  roots  of  a  thrifty 
cornstalk,  if  laid  end  to  end,  would  extend  a  mile.  In  the 
development  of  the  root  system,  a  great  deal  depends  upon 
external  conditions.  In  a  poor,  dry  soil,  the  roots  have  to 
travel  farther  in  search  of  a  livelihood,  and  so  a  larger  system 
has  to  be  developed  than  in  a  more  favorable  location. 


THE  ROOT  79 

Practical  Questions 

1.  Which  is  better  to  succeed  a  crop  of  turnips  on  the  same  land,  hay 
or  carrots?     (81.) 

2.  Write  out  what  you  think  would  be  a  good  rotation  for  four  or 
five  successive  crops  based  on  the  forms  of  the  roots. 

3.  Study  the  following  rotations  and  give  your  opinion  about  them, 
on  the  same  principle.  Suggest  any  improvements  that  may  occur  to 
you,  and  give  a  reason  for  the  change.  Beets,  barley,  clover,  wheat; 
cotton,  oats,  peas,  corn;  oats,  melons,  turnips;  cotton,  oats,  corn  and 
])eas  mixed,  melons ;   cotton,  hay,  corn,  peas. 

4.  Give  three  good  reasons  in  favor  of  a  rotation  over  a  single-crop 
system.     (24,  60,  62,  81.) 

5.  Which  will  require  deeper  tillage,  a  bed  of  carrots  or  one  of  straw- 
berries?    (81.) 

6.  Explain  why  some  plants  keep  green  and  fresh  when  the  surface 
of  the  soil  is  dry,  while  others  wilt  or  die.     (81,  89.) 

7.  Which  will  better  withstand  drought,  a  crop  of  alfalfa  or  one  of 
Indian  corn  ?     Why  ?     (81 . ) 

8.  Which  will  interfere  less  with  the  trees  if  planted  in  an  orchard, 
beets  or  onions  ?     (81.) 

9.  Ought  a  crop  of  hemp  and  tobacco  to  succeed  each  other  on  the 
same  land?     (81,89.) 

10.  Why  does  a  gardener  manure  a  grass  plot  by  scattering  the  ferti- 
lizer on  the  surface,  while  he  digs  around  the  roses  and  lilacs  and  deposits 
it  under  ground  ?     (81.) 

11.  Do  the  adventitious  roots  of  such  climbers  as  ivy  and  trumpet  vine 
draw  any  nourishment  from  the  objects  to  which  they  cling?     (83-88.) 

12.  How  can  you  tell  ? 

13.  Do  partial  dependents  of  this  kind  injure  trees  by  climbing  upon 
them;    and  if  so,  how?     (87,88.) 

14.  What  is  the  use  of  the  aerial  roots  of  the  scuppernong  grape  ?     (88.) 

15.  Is  the  resurrection  fern  {Poly-podium  incanum),  that  grows  on  tree 
trunks  in  our  Southern  States,  a  parasite  or  an  air  plant?     (87.) 

16.  On  what  plants  in  your  neighborhood  does  mistletoe  grow  most 
abundantly  ?     Dodder  ? 

17.  Is  mistletoe  injurious  to  the  host?     (85.) 

18.  Name  some  plants  that  are  propagated  mainly,  or  solely,  by  roots 
and  cuttings. 

19.  Where  do  aerial  roots  get  their  nourishment  ?     (88.) 

20.  Would  they  be  of  any  use  to  a  plant  in  a  very  cold  or  dry  climate  ? 

21.  Where  should  manure  be  placed  to  benefit  a  tree  or  shrub  with 
wide-spreading  roots  ?     (66,  89.) 


80  PRACTICAL  COURSE  IN  BOTANY 

22.  Is  it  a  wise  practice  to  mulch  a  tree  by  raking  up  dead  leaves  and 
piling  them  around  the  base  of  the  trunk,  as  is  often  done  ?  Why,  or  why 
not?     (66,89.) 

Field  Work 

(1 )  Examine  the  underground  parts  of  hardy  winter  herbs  in  your  neigh- 
borhood, also  of  any  weeds  or  grasses  that  are  particularly  troublesome, 
and  see  if  there  is  an3'thing  about  the  structure  of  these  parts  to  account 
for  their  persistence.  Note  the  difference  between  roots  of  the  same  species 
in  low,  moist  places  and  in  dry  ones ;  between  those  of  the  same  kind  of 
plants  in  different  soils;  in  sheltered  and  in  exposed  situations.  Study 
the  direction  and  position  of  the  roots  of  trees  and  shrubs  with  reference 
to  any  stream  or  body  of  water  in  the  neighborhood.  (The  elm,  fig, 
mulberry,  and  willow  are  good  subjects  for  such  observations.)  Notice 
also  whether  there  is  any  relation  between  the  underground  parts  and  the 
leaf  systems  of  plants  in  reference  to  drainage  and  transpiration. 

(2)  Observe  the  effect  of  root  pull  upon  low  herbs.  Look  along  washes 
and  gullies  for  roots  doing  the  office  of  stems,  and  note  any  changes  of 
structure  consequent  thereon.  Study  the  relative  length  and  strength 
of  the  root  systems  of  different  plants,  with  reference  to  their  value  as 
soil  binders,  or  their  hurtfulness  in  damaging  the  walls  of  cellars,  wells, 
sewers,  etc.  Dig  your  trowel  a  few  inches  into  the  soil  of  any  grove 
or  copse  you  happen  to  visit,  note  the  inextricable  tangle  of  roots,  and 
consider  the  fierce  competition  for  living  room  in  the  vegetable  world  that 
it  implies. 

(3)  Tests  might  be  made  of  the  different  soils  in  the  neighborhood  of 
the  schoolhouse  by  planting  seeds  of  various  kinds  and  noting  the  rate  of 
germination;  first,  without  fertilizers,  then  by  adding  the  different  ele- 
ments in  succession  to  see  what  is  lacking.  The  field  for  study  suggested 
by  this  subject  is  almost  inexhaustible. 


CHAPTER  IV.     THE   STEM 
I.    FORMS    AND    GROWTH    OF    STEMS 

Material.  —  Vigorous  young  hop  or  beau  seedlings  grown  in  pots ; 
a  fresh  daudehon  stalk ;  a  stem  of  pea,  squash,  cucumber,  grape,  or  passion 
flower  vine,  with  tendrils. 

Appliances.  —  A  bowl  of  fresh  water ;  rods  of  different  sizes  and 
smoothness  for  testing  the  hold  of  climbers. 

Experiment  54.  To  show  the  movements  of  twining  stems.  — 
Raise  a  young  hop  or  bean  seedling  in  the  schoolroom  and  allow  it  to  grow 
about  two  decimeters  —  8  to  10  inches  —  in  length  before  providing  it 
with  a  support.  Does  the  stem  form  any  coils?  Bring  it  in  contact 
with  a  suitable  upright  support  and  watch  for  a  day  or  two.  What 
happens  ?  Notice  whether  it  starts  to  coil  from  right  to  left  or  from  left 
to  right  and  see  if  you  can  coax  it  to  turn  in  the  opposite  direction.  When 
it  has  reached  the  end  of  its  stake,  allow  it  to  grow  about  five  centimeters 
(two  inches,  approximately)  beyond,  and  watch  the  revolution  of  the  tip. 
Cut  a  hole  through  the  center  of  a  piece  of  cardboard  about  14  centi- 
meters (five  to  six  inches)  in  diameter,  slip  it  over  the  loose  end  of  the  stem, 
and  fasten  it  to  the  stake  in  a  horizontal  position,  with  a  pin.  Note  the 
position  of  the  stem  tip  at  regular  intervals  and  mark  on  the  cardboard ; 
how  long  does  it  take  to  complete  a  revolution  ?  Does  it  continue  to  coil, 
or  to  coil  as  readily,  after  leaving  its  stake  as  before  ?  What  would  you 
infer  from  this  as  to  the  effect  of  contact  in  stimulating  it  to  coil  ? 

Find  out  by  experiment  if  it  can  climb  well  by  means  of  a  glass  or  other 
smooth  rod ;  by  a  fine  wire ;  a  broomstick ;  a  large,  smooth  post.  See 
whether  it  does  better  on  a  horizontal  or  an  upright  support. 

Experiment  55.  To  illustrate  the  coiling  of  stems.  —  Run  a 
gathering  thread  in  one  side  of  a  narrow  strip  of  muslin  and  notice  how 
the  ruffle  thus  drawn  will  curl  into  a  spiral  when  allowed  to  dangle  from 
the  needle.  Can  you  think  of  any  cause  that  might  act  on  a  stem  in  the 
same  way  ?  Suppose,  for  instance,  that  one  side  should  grow  faster  than 
the  other ;  what  would  be  the  effect  ?     (54.) 

Split  the  stem  of  a  fresh  dandelion,  or  other  herbaceous  scape,  longi- 
tudinally, and  innnerse  it  in  a  pan  of  fresh  water  for  a  few  minutes.  Notice 
how  the  two  halves  curve  outward,  or  even  coil  up  like  the  strip  of  muslin. 
This  is  due  to  the  tension  caused  by  the  more  rapid  absorption  of  the 

81 


82 


PRACTICAL  COURSE  IN  BOTANY 


thinner  walled  cells  of  the  internal  tissues.  These,  when  relieved  ot  the 
resistance  of  the  thicker  walled  outer  tissues,  swell  on  their  free  side,  but 
are  held  back  on  the  other  by  the  non-absorbent  outer  parts,  as  one  side 
of  the  muslin  ruffle  was  held  by  the  gathering  thread. 

Experiment  56.  To  find  out  whether  the  direction  of  stem 
GROWTH  IS  INFLUENCED  BY  LIGHT.  —  Placc  two  rapidly  growing  young 
pea,  bean,  sunflower,  or  squash  plants,  each  with  several  well-developed 
leaves,  in  a  room  or  box  with  a  light  exposure  on  one  side  only.  After  two 
or  three  days,  notice  the  position  of  the  stems  in  regard  to  the  light.  Does 
either  one  show  a,  more  decided  inclination  toward  it  than  the  other  ? 

Experiment  57.  Is  the  light  relation  of  the  stem  influenced 
BY  the  leaves?  —  Cut  the  leaves  from  one  of  the  plants  used  in  Exp.  56, 
covering  the  cut  surfaces  with  vaseline  to  prevent  "bleeding";  reverse 
the  positions  of  both  with  regard  to  the  light,  and  watch  for  two  or  three 
days.  In  which  is  the  response  to  light  the  more  rapid  ?  What  does  this 
indicate  as  one  object  of  the  stem  in  seeking  light?  What  is  the  best 
position  of  a  stem,  ordinarily,  for  getting  its  leaves  into  the  light  ? 

go.  Classification.  —  Stems  are  classed  according  to 
(1)  duration,  as  annuals,  biennials,  and  perennials;  (2)  with 

reference  to  hardness  or 


1 

softness  of  structure,  as 
herbaceous  and  woody; 
(3)  in  regard  to  position 
and  direction  of  growth, 
as  erect,  prostrate,  climb- 
ing, inclined,  dechned, 
underground,  etc. 

Qi.  Annuals  complete 
their  life  cycle  in  a 
single  season  and  then 
die  down  as  soon  as  they 
have  perfected  their 
seed.  Many  of  our  most 
troublesome  weeds  be- 
long to   this   class   and 

might  be  exterminated  by  the  simple  expedient  of  mowing 

them  down  before  their  time  of  flowering. 


Fig.  92.  —  Stems  of  red  oak  and  '. 
have  grafted  themselves. 


THE  STEM 


83 


92.  Biennials,  as  the  name  implies,  live  for  two  years. 
Their  energy  during  the  first  season  is  spent  chiefly  in  laying 
by  a  store  of  nourishment, 
usually  in  the  tissues  of 
fleshy  roots  (70).  By  this 
means  they  get  a  good  start 
in  the  second  season  and 
mature  their  seeds  early. 
Many  of  our  common  gar- 
den vegetables,  such  as  tur- 
nips, carrots,  parsnips,  and 
cabbage,  belong  to  this 
class.  Where  is  the  nour- 
ishment stored  in  the  cab- 
bage? 

93.  Perennials  are  plants 
that  live  on  indefinitely,  like 
most  of  our  forest  trees 
and  woody-stemmed  shrubs. 
Woody  stems  are  usually  perennial  and  may  live  for  hun- 
dreds and  even  thousands  of  years,  as  those  of  the  giant 
sequoias  of  California,  and  the  famous  chestnut  of  Mt. 
Etna. 

94.  Herbaceous  stems  are  more  or  less  succulent  and  die 
down  after  fruiting.  They  are  usually  annuals,  though  some 
kinds,  like  the  garden  geraniums  and  the  common  St.-John's- 
wort,  show  a  tendency  to  become  woody,  especially  at  the 
base,  and  live  on  from  year  to  year.  Others,  such  as  the 
hawkweed  and  dahlia,  die  down  above  ground  in  winter, 
but  are  enabled  to  keep  their  underground  parts  alive  indefi- 
nitely, through  the  nourishment  stored  in  them,  and  are 
thus  perennial  below  ground  and  annual  above.  Woody- 
stemmed  annuals,  such  as  the  cotton  and  castor  oil  plant, 
are  not,  properly  speaking,  herbs.  In  the  tropical  countries 
to  which  they  belong  they  are  perennial  shrubs,  or  even 
small   trees,  but  on  being   transplanted  to  colder  regions 


Fig.  93. —  A  liicimial  plant,  mullein,  in 
winter  conditii^n  with  stem  reduced  to 
little  more  than  a  disk  supporting  a  rosette 
of  leaves.  Notice  how  close  they  cling  to 
the  earth,  and  compare  them  with  their 
fruiting  condition  a  few  months  later  aa 
shown  in  Fig.  237. 


84 


PRACTICAL  COURSE  IN  BOTANY 


have  been  compelled  to  take  on  the  annual  habit  as  an 
adaptation  to  climate. 

95.   Direction  and  habit  of   growth.  —  As  to  manner  of 
growth,  there  are   many  forms,  from  the  upright  boles  of 


Fig.  94.  —  Orange  hawk- 
weed  with  runners. 


Fig.  95.  —  Prostrate  stem  of  Lycopodium 
with  assurgent  branches. 


the  beech  and  pine  to  the  trailing,  prostrate,  and  creeping 
stems  of  which  we  have  examples  in  the 
running  periwinkle,  the  prostrate  spurge 
and  the  creeping  partridge  berry  {Mitchella 
repens),  respectively.  Trailing  and  pros- 
trate stems  are  very  apt  to  become 
creepers  by  the  development  of  adventi- 
tious roots  at  their  nodes  wherever  they 
come  in  contact  with  the  soil.  The  root- 
ing stems  of  dewberries,  the  runners  and 
stolons  of  strawberries  and  currants,  are 
familiar  examples. 

Between  the  extremes  of  prostrate  and 
upright,  stems  may  be  inclined  or  bent  in 
various  degrees.  As  shown  in  Fig.  96, 
there  are  two  modes  of  inclination :  assur- 
gent, a,  from  the  prostrate,  p,  toward  the 
upright,  e ;  and  declined,  d,  from  the  upright 


Fig.  9G.  —  Diagram 
of  stem  growth :  p.v, 
surface  of  the  ground  ; 
e,  erect  position ;  d, 
declined  ;  a,  assurgent ; 
V,  prostrate ;  w,  ver- 
tical direction  under- 
ground. 


THE  STEM 


85 


toward  the  prostrate.  Below  the  surface,  ps,  occur  only 
underground  stems.  Is  the  prostrate  habit  an  advantageous 
one  for  Hght  exposure  ?  Can  you  think  of  any  compensat- 
ing advantages  a  plant  might  derive  from  it ;  for  example, 
in  regard  to  warmth  and  moisture  ? 

96.  Climbing  stems.  — ■  These  are  such  as  lift  themselves 
from  the  ground  and  attain  the  advantages  of  the  upright 
position  by  clinging  to  supports  of 
various  kinds  —  usually,  in  a  state 
of  nature,  the  stems  and  boughs  of 
other  plants.  The  means  of  climb- 
ing may  be  :  (1)  by  merely  leaning 
upon  or  propping  themselves  up  by 
the  aid  of  the  supporting  object — ex- 
amples, the  rose,  wistaria,  star  jessa- 
mine {Jasminum  officinalis) ;  (2)  by 
coiling  their  main  axes  spirally 
around  the  support  —  hop,  bean, 
morning-glory ;  (3)  by  means  of  ad- 
ventitious roots  —  poison  ivy,  com- 
mon English  ivy,  trumpet  vine 
( Tecoma  radicans) ;  (4)  by  organs  specially  developed  for 
the  purpose,  called  tendrils  —  gourd,  cucumber,  grape,  pas- 
sion flower. 

97.  Tendrils.  —  The  part  assigned  to  do  the  work  of  climb- 
ing may  be  a  secondary  branch,  a  flower  stem,  a  leafstalk,  a 
leaf,  a  leaflet,  or  a  group  of  leaflets  (Fig.  98).  Tendrils  behave 
in  general  very  much  like  twining  stems,  except  that  they 
are  more  sensitive  and  respond  more  quickly  to  any  cause 
that  may  influence  their  movement.  While  young,  their 
tips  revolve  just  as  do  the  tips  of  twining  stems,  until  they 
meet  with  an  object  round  which  they  can  coil.  When  this 
happens,  not  only  the  part  in  contact  with  the  object  coils, 
but  the  free  part  between  it  and  the  main  axis  will  usually 
respond  by  twisting  itself  into  a  helix  (Fig.  99).  As  the 
distance  between  the  base  and  tip  of  the  tendril  is  shortened 


A 
Fig.  97.  —  Twining  stems  : 

A,  hop  twining  with  the  sun  ; 

B,  convolvulus  twining  against 
the  sun. 


86 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  98. — Leaf  of  common  pea, 
showing  upper  leaflets  reduced  to 
tendrils. 


by  coiling,  the  body  of  the  plant 
is  drawn  upward  proportionally. 
It  will  be  observed  that  the  helix 
is  interrupted  at  one  or  more 
points,  above  and  below  which 
the  coils  turn  in  opposite  direc- 
tions. This  is  because  the  ten- 
dril is  attached  at  both  ends  and 
cannot  adjust  itself  to  the  oppo- 
site strains  of  torsion.  Twist 
with  your  fingers  a  piece  of  tape 
so  attached,  and  you  will  see 
that  on  one  side  of  your  hand  it 
turns  from  right  to  left  and  on 
the  other  from  left  to  right. 

98.  The  cause  of  twining.  — 
Botanists  are  not  fully  agreed 
on  this  point.  The  explanation 
most  generally  accepted  at  present  is  that  the  twining  of 
stems  is  due  to  the  combined  action  of  lateral  and  negative 

geotropism(51).     The  first 

^^^^^-^"^^^^   causes   one    side   to   grow 

more  rapidly  than  the  other, 
thus  forming  a  succession  of  coils,  while  the 
second,  by  stimulating  the  upward  growth 
of  the  axis,  stretches  it  into  a  spiral,  and  in 
this  way  draws  it  more  tightly  round  the 
support.  For  this  reason  twining  stems  do 
best  on  an  upright  support. 

In  tendrils,  the  twining  is  thought  to  be 
due  not  to  gravity,  but  to  contact  with  a 
soHd  body,  which,  by  inducing  unequal  de- 
velopment on  opposite  sides  of  the  tendril, 
of  a  passion  flower   causes  it  to  tum  about  an  available  object, 
transformed    into   ^he  coiliug  of  the  free  part  of  the  twining 

tendrils.     {After  .        "  -^  " 

Gray.)  Organ  IS  in  response  to  the  stimulus  trans- 


FiG.  99. 


THE   STEM 


87 


mitted  from  the  part  in  contact  —  stimulus,  in  this  sense, 
denoting  the  influence  of  any  external  agent  that  calls  forth 
a  responsive  adjustment  on  the  part  of  the  plant. 

99.  The  object  of  the 
various  habits  of  stem 
growth.  —  To  bring  the 
growing  parts  of  the  plant 
into  the  best  possible  rela- 
tions with  light  and  air  is 
one  of  the  special  func- 
tions of  the  stem,  and  the 
various  habits  of  growth 
described  in  this  section 
have  been  developed  with 
reference  to  this  function. 
In  the  case  of  prostrate 
and  underground  stems 
other  factors  may  intervene ; 
can  you  name  some  of  the 
causes  that  might  influence 
the  position  of  the  stem  in 
such  cases  ? 


i'lG.  lUU.  —  tjhowiiig  the  ecouoniy  of 
labor  and  building  material  effected  by  the 
climbing  habit.  Notice  how  the  g^ape^'ine 
coils  like  an  anaconda  around  the  tree 
boles,  and  overtops  their  tallest  branches. 
Compare  the  diameter  of  the  vine  with  that 
of  the  trees. 


Practical  Questions 

1.  Why  is  the  normal  direction  of  most  stems  upright?     (Exp.  56.) 

2.  Name  a  dozen  woody-stemmed  plants;  a  dozen  with  herbaceous 
stems. 

3.  Name  all  the  plants  you  can  think  of  that  have  prostrate  st^ms,  or 
leaf  rosettes  that  hug  the  earth,  like  mullein  and  dandelion.  Which  of 
these  are  wintergreen  plants  ?     Which  are  hot-weather  growers  ? 

4.  Can  you  explain  in  what  ways  both  hot-weather  and  cold-weather 
plants  may  be  advantaged  by  the  habit  of  clinging  close  to  the  earth  ? 
(94,  95.) 

5.  Is  there  any  difference  in  the  height  of  the  stem  of  a  dandelion  flower 
and  a  dandelion  ball  ? 

6.  Of  what  advantage  is  this  to  the  plant?     (Exp.  17.) 

7.  Name  all  the  means  you  can  think  of  by  which  a  stem  may  climb, 
and  give  an  example  of  each. 


88  PRACTICAL  COURSE  IN  BOTANY 

8.  Why  do  we  support  peas  with  brush,  and  hops  or  beans  wnth  poles? 
(98 ;  Exp.  54.) 

9.  Are  the  vines  of  gourds,  watermelons,  squashes,  and  pumpkins 
normally  climbing  or  prostrate  ?     How  can  you  tell  ?     (96,  97.) 

10.  Why  does  not  the  gardener  pro\^ide  them  with  poles  or  treUises  to 
climb  on  ? 

11.  Do  twining  plants  grow  equally  well  on  horizontal  and  upright 
supports?     (98;  Exp.  54.) 

12.  If  there  is  any  difference,  which  do  they  seem  to  prefer? 

13.  Can  you  give  any  reasons  for  thinking  that  the  clunbing  habit 
might  lead  to  parasitism?     (83,  85,  87.) 

14.  What  method  of  climbing  would  be  most  favorable  to  the  develop 
ment  of  such  a  habit  ?  (Suggestion  :  What  mode  of  climbing  brings  the 
stem  into  closest  contact  with  its  support?) 

15.  Name  some  plants  the  stems  of  which  are  used  as  food. 

16.  Name  some  from  which  gums  and  medicines  are  obtained. 

17.  Explain  how  it  can  benefit  a  plant  to  have  its  leaves,  or  some  of 
them,  modified  into  tendrils.     (99.) 

18.  In  what  way  is  the  loss  of  the  normal  function  of  the  leaves  so  modi- 
fied, compensated  for?     (Exp.  57.) 

19.  Suppose  the  vine  shown  in  Fig.  100  had  to  lift  itself  without  the  aid 
of  a  support ;  could  it  reach  the  same  height  and  carry  the  same  weight 
of  foliage  and  flowers  with  the  same  expenditure  of  labor  and  building 
material  ? 

n.    MODIFICATIONS    OF   THE    STEM 

Material.  —  A  shoot  of  asparagus ;  thorny  branches  of  locust,  plum, 
or  haw ;  a  cactus  plant ;  bulbs  of  lily  and  hyacinth  or  onion ;  tubers  of 
potato ;  rootstocks  of  iris,  fern,  or  violet.  If  fresh  specimens  are  not  acces- 
sible, dried  rootstocks  of  the  sweet  flag  and  Florentine  iris  may  be  obtained 
at  the  drug  stores  under  the  names  of  calamus  and  "orris"  root. 

100.  How  to  recognize  modified  parts.  —  Stems,  like 
roots,  are  often  modified  to  serve  other  than  their  normal 
purpose,  and  in  adapting  themselves  to  these  new  functions 
they  sometimes  undergo  such  changes  of  form  and  structure 
that  it  would  be  impossible  to  recognize  their  true  nature 
from  appearances  alone.  The  safest  tests  in  such  cases 
are :  (1)  by  a  comparison  of  the  parts  of  the  modified  struc- 
ture with  those  of  known  organs  of  the  same  kind ;  and  (2)  by 
observing  its   position  in  reference   to   other  parts.     For 


THE   STEM 


89 


instance,  we  know  that  the  stem  is  the  part  of  the  plant  which 
normally  bears  leaves  and  flowers,  and  if  either  of  these, 
or  if  the  small  scales  which  often  take  the  place  of  leaves, 
are  found  growing  on  any  plant  structure,  we  may  usually 
take  for  granted  that  it  is  a  stem.  Then,  again,  as  will  be 
shown  in  the  next  chapter,  buds  and  branches  naturally 
appear  only  at  the  nodes,  in  or  near  the  axil,  or  inner  angla 
made  by  a  leaf  with  the  stem.  Hence,  if  you  see  any  growth 
springing  from  such  a  position,  you  may  generally  conclude 
it  to  be  a  stem. 

loi.  Stems  as  foliage.  —  The  connection  between  stem 
and  leaf  is  so  intimate  that  we  need  not  be  surprised  to  find 
a  frequent  interchange  of  function 
between  them,  the  leaf,  or  some  part 
of  it,  doing  the  work  of  the  stem 
(Fig.  98),  the  stem  more  often  taking 
upon  itself  the  office  of  the  leaf.  A 
conmion  example  is  the  garden  aspar- 
agus. Examine  one  of  the  young 
shoots  sold  in  the  market,  and  notice 
that  it  bears  a  number  of  small  scales 
in  place  of  leaves.  On  an  older 
shoot  that  has  gone  to  seed,  the 
green,  threadlike  appendages,  which 

^  '  I  i'  G      >  Pjq    101.  —  Stem-leaves 

are  usually  taken  for  foliage,  will  be  (ciadophyiis)  of  a  mscus,  bear- 
found  to  spring  each  from  the  axil  '^^^°''''''- 
of  one  of  these  scales.     What,  therefore,  are  we  to  conclude 
that  it  is  ? 

In  the  butcher's-broom  of  Europe,  the  transformation  has 
gone  so  far  that  the  branches  of  the  stem  have  assumed  the 
flattened  appearance  of  leaves  (Fig.  101),  but  their  real 
nature  is  evident  both  from  their  position  in  the  axils  of 
leaf  scales,  and  from  the  fact  that  they  bear  flower  clusters 
in  the  axil  of  a  scale  on  their  upper  face.  Another  example 
of  this  sort  of  modification  is  seen  in  the  pretty  little  myr- 
siphyllum  of  the  greenhouses  (wrongly  called  smilax),  which 


90 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  102.  —  Thorn  branches  of 
Holocanthn  Emoryi,  a  plant  growing 
in  arid  regions. 


is  so  much  used  for  decoration. 
The  deUcate  green  blades  are 
merely  altered  stems,  shortened 
and  flattened  to  simulate  leaves. 
102.  Weapons  of  defense. — 
Conspicuous  examples  of  these 
are  the  bristling  thorns  of  the 
honey  locust.  Is  their  frequent 
branching  any  indication  of  their 
real  nature  ?  Does  it  prove  any- 
thing, or  must  you  look  for  other 
evidence?  WTiat  further  indi- 
cations might  you  expect  to 
find,  if  they  are  true  branching 
stems?  (100.)  On  old  haw, 
plum,  crab,  and  pear  trees,  stems  can  be  found  in  all  stages 
of  transition,  from  stubby,  ill-developed  branches,  to  well- 
defined  thorns. 

103.  Storage  of  nourishment.  —  This  is 
one  of  the  most  frequent  causes  of  modifi- 
cation in  both  roots  and  stems.  Of  stems 
that  grow  above  ground,  the  sugar  cane 
probably  comes  first  in  economic  importance 
on  this  account.  In  hot,  arid  regions,  where 
the  moisture  drawn  from  the  earth  would, 
during  prolonged  drought,  be  too  rapidly 
dissipated  by  an  expanded  surface  of  leaves, 
the  whole  plant,  as  in  the  case  of  the  cactus, 
is  sometimes  compacted  into  a  greatly  thick- 
ened stem,  which  fills  the  triple  office  of  leaf, 
stalk,  and  water  reservoir. 

104.  The  uses  of  underground  stems.  — 
It  is  in  these  that  the  storage  of  nourishment 
most  frequently  takes  place,  and  the  modi- 
fications that  stems  undergo  for  this  purpose 
are  iji   some  cases  so  great  that  their  real 


Fig.  103. — Melon 
cactus,  showing 
greatly  condensed 
stem  for  the  storage 
and  preservation  of 
moisture. 


THE  STEM 


91 


Fig.  104.  —  Root- 


nature  becomes  apparent  only  after  a  careful  examination. 
But  while  the  chief  function  of  underground  stems  is  the 
storage  of  nourishment,  they  serve  other  purposes  also.  In 
plants  requiring  a  great  deal  of  moisture, 
like  the  ferns,  and  in  others  growing  in  dry 
places  and  needing  to  husband  moisture 
carefully,  Uke  the  blackberry  lily,  under- 
ground stems  may  be  useful  in  preventing 
the  too  rapid  evaporation  that  would  take- 
place  through  aerial  stems.  Defense  against 
frost,  cold,  heat,  and  other  dangers,  as  well- 
as  quickness  of  propagation,  are  also  attained 
or  assisted  by  this  means. 

105.  Rootstocks  and  rhizomes.  —  From  a 
prostrate  stem  like  that  shown  in  Fig.  95  to  a 
creeping  rootstock  like  the  one  in  Fig.  104,  the  stock    of    creeping 
transition  is  so  easy  that  we  find  no  difficulty  ^^'^'^  ^''^^^' 

in  accounting  for  it.  From  the  prostrate  rootstock  to  the 
thickened  storage  rhizome  (Fig.  105)  of  such  plants  as  the  iris, 
puccoon,  bulrush,  and  Solomon's-seal,  is  a  longer  step,  but 
the  bud  with  its  leaf  scales  at  the  growing  tip,  a,  the  remains 
of  the  flower  stem  at  the  node,  b,  and  the  roots  from  the  under 
surface  sufficiently  indicate  its  na- 
ture. The  peculiar  scars  from  which 
CI  the  Solomon's-seal  takes  its  name 
-^^OWfl^L  ^^^    caused    by  the     falling    away 

Fig.  105^  Rhlme  of  Sol-  ^^^^    ^e^^     ^^     t^^.  Aowering     Stem 
omon's-seal :   a,  growing  bud  at  of  the  SCaSOU  after  its  WOrk    is  doue, 

Lt™';;flower"im;°!:'':raS  leaving  behind  the  node  of  the  un- 
of  old  stems.  (After  Gray.)  dcrgrouud  stcui  from  which  it  Orig- 
inated. In  this  way  the  rhizome  lives  on  indefinitely, 
growing  and  increasing  at  one  end  as  fast  as  it  dies  at 
the  other.  Test  a  little  of  the  substance  of  the  rhizome 
with  iodine.  Of  what  does  it  consist?  Of  what  use  is  it 
to  the  plant? 

106.  The  tuber.  —  A  still  further  thickening  and  shorten- 


92 


PRArTTCAL  COURSE  IN  BOTANY 


ing  of  the  rhizome  gives  rise  to  the  tuber,  of  which  the 
potato  and  the  Jerusalem  artichoke  are  famiUar  examples. 
Can  you  give  any  evidence  to  show  that  the  potato  is  a 

modified  stem?  Find  the 
})oint  of  attachment  of  the 
tuber  to  its  stem  and  stantl 
it  on  this  end,  which  is  its 
natural  base.  Notice  that 
the  eye  sits  in  the  axil  of 
the  little  scale  that  forms 
the  eyelid.  What  does  the 
scale   represent?     "WTiat   is 


Fig.  U)( 


)cr  showing  Iciiti- 


cels,  A,  A,  or  pores  for  air  ou  the  surface  ; 
<S,  leaf  scale,  or  scar. 


the   eye?     (100.)     Do    the 
scales  occur  in  any  regular 

order  —  that  is,  opposite,  or  alternating  with,  each  other,  like 

the  leaves  on  a  stem  ?     Look  on  the  surface  for  a  number  of 

small,  lens-shaped  dots  (A,  A,  Fig.  106)  scattered  irregularly 

over  it.     These  are  aerating  pores  called  lenticels,  and  are 

found  in  most  dicotyl 

stems.     Does      their 

presence  help  to  throw 

light  on  the  real  nature 

of  the  tuber?     If  any 

sprouts  occur  on  your 

specimen,     where     do 

they  originate?    Where 

do   buds   and   sprouts 

originate     on     plants 

above  ground  ?     Make 

a  sketch  of  the  outside 

of  a  potato,    showing 

the  lenticels,  eyes,  and 

scales,  or  the  scars  left 

by  the  scales  in  case  they  have  fallen  away,  as  has  probably 

happened,  if  your  specimen  is  an  old  one. 

Cut  a  small  slice  from  the  stem  end  of  two  potatoes,  stand 


Figs.  107,  108.— 
Transverse  and  longi- 
tudinal sections  of  the 
potato:  A,  skin;  B, 
cortical  layer  ;  C,  outer 
pith  layer  ;  D,  inner  pith 
layer. 


THE   STEM  93 

them  in  coloring  fluid  for  four  or  five  hours,  then  divide  into 
cross  and  vertical  sections,  as  shown  in  Figs.  107,  108,  and 
draw,  labeling  the  parts  that  you  can  make  out.  Through 
which  has  the  liquid  ascended  most  rapidly?  Test  with 
iodine  and  find  out  in  which  part  nourishment  is  most  abun- 
dant. It  is  this  abundant  store  of  food  that  makes  the 
potato  such  a  valuable  crop  in  cold  countries  like  Norway 
and  Iceland,  where  the  seasons  are  too  short  to  admit  of  the 
slow  process  of  developing  the  plant  from  the  seed. 

Compare  a  common  potato  with  a  sweet  potato.  Are 
there  any  eyes  or  buds  on  the  latter  ?  Is  there  a  scale  below 
them?  Do  they  occur  in  any  regular  order?  Do  you  see 
any  lenticels?  The  common  potato  and  the  sweet  potato 
are  both  tubers ;  can  you  give  some  of  the  reasons  why  the 
one  is  regarded  as  a  modi- 
fied branch,  and  the  other 
as  a  root?  (100.)  Com- 
pare their  food  contents; 
which  contains  most 
starch?  Which  most 
sugar?  How  can  you 
judge  about  the  sugarwith-       Fig.  i09.-scaiy         Fig  no. -  Scaiy 

•■       *       ,  .      ,   ,      To  bud  of  oak,  enlarged.       bulb  of  lily  (Gray). 

out  a  chemical  test  ( 

107.  The  bulb  is  a  form  of  underground  stem  reduced  to  a 
single  bud.  Get  the  scaly  bulb  of  a  lily,  and  sketch  it  from 
the  outside  and  in  cross  and  vertical  section.  Compare  it 
with  the  scaly  winter  buds  of  the  oak  and  hickory,  or  other 
common  deciduous  tree.  Make  an  enlarged  sketch  of  the 
latter  on  the  same  scale  as  the  lily  bulb,  and  the  resemblance 
will  at  once  become  ai:)parent.  The  scales  of  the  bulb  are,  in 
fact,  only  thick,  fleshy  leaves  closely  packed  around  a  short 
axis  that  has  become  dilated  into  a  flat  disk.  From  the  center 
of  the  disk,  which  is  the  terminal  node  of  this  transformed 
stem,  rises  the  flower  stalk,  or  scape,  as  it  is  called,  of  the 
season.  After  blossoming,  the  scape  perishes  with  its  bulb, 
and  their  place  is  taken  by  new  ones  which  are  developed 


94         PRACTICAL  COURSE  IN  BOTANY 

from  the  axils  of  the  scales,  thus  revealing   their  leaflike 

nature. 

That  bulbs  are  only  modified  buds  is  further  shown  by 

the  bulblets  that  sometimes  appear  among  the  flowers  of  the 
onion,  and  in  the  leaf  axils  of  certain  lilies. 
They  never  develop  into  branches,  but  drop 
off  and  grow  into  new  plants  just  as  the 
subterranean  bulbs  do. 

The  bulbs  of  the  onion  and  hyacinth  are 
still  further  modifications,  in  which  the  scales 
consist  of  the  thickened  bases  of  leafstalks 
that  are  dilated  until  each  one  completely 

of  rron^n'dhS    envelops  the  growing  parts  within. 

lengthwise,  showing        io8.   Moiphology   is   the  part  of  botany 

the     base    enlarged      ,i      ,      ,  ,  c    ir.  •    •         r  j 

into  the  coat  of  a  that  treats  01  the  origm,  lorm,  and  uses 
*'""'•  of  the  different   organs   of  plants,  and  of 

the  modifications  they  undergo  in  adapting  themselves  to 
changes  of  condition  or  function.  Organs  or  parts  that 
have  the  same  origin  but  have  become  adapted  to  dif- 
ferent functions,  like  the  flattened  stems  of  the  butcher's- 
broom  or  the  bulb  scales  of  the  lily,  are  said  to  be 
homologous;  those  that  are  different  in  origin  but  adapted 
to  the  same  function,  as  the  sweet  and  common  pota- 
toes, are  analogous.  In  other  words,  homologous  organs 
are  morphologically  alike,  but  may  be  physiologically  dif- 
ferent;  analogous  organs  are  alike  physiologically,  but 
differ  morphologically. 

109.  Economic  value  of  stems.  —  We  probably  get  a 
greater  variety  of  economic  products  from  the  stem  than 
from  any  other  part  of  the  plant.  Consider  the  vast 
amount  of  food  stored  in  underground  stems  like  the  potato  ; 
the  resins,  gums,  and  sugar  found  in  the  sap  of  plants 
like  the  sugar  cane,  the  pine,  and  India-rubber  trees;  the 
medicines,  dyes,  and  extracts  obtained  from  the  tissues  ;  the 
valuable  fibers,  such  as  flax,  jute,  and  hemp,  furnished  by 
the  bast;  the  wood  pulp  for  making  paper;  and  the  timber 


THE  STEM  95 

for  building  and  furnishing  our  houses  that  we  get  from  the 
woody  trunks  of  trees.  When  we  think  of  all  these  things, 
it  seems  hardly  possible  to  overestimate  the  importance  of 
this  part  of  the  vegetable  kingdom  to  man,  or  to  exert 
ourselves  too  strenuously  to  regulate  and  prevent  the  de- 
struction of  these  invaluable  natural  resources. 


Practical  Questions 

1.  Would  you  judge  from  the  observations  made  in  the  foregoing  sec- 
tion, that  the  work  of  an  organ  determines  its  form,  or  that  the  form  deter- 
mines its  work  ?     (99,100,108.) 

2.  Which  is  the  more  important,  form  or  function  ? 

3.  Name  some  plants  that  are  propagated  by  rootstocks ;  by  runners 
or  stolons ;  by  rhizomes ;  by  tubers ;  by  bulbs. 

4.  What  is  the  advantage  of  propagating  in  this  way  over  planting  the 
seed?     (104,  106.) 

5.  Mention  any  other  advantages  that  the  various  plants  named  may 
gain  from  the  development  of  their  underground  parts.     (104.) 

6.  What  makes  the  nut  grass  so  troublesome  to  farmers  in  some  parts 
of  the  country  ? 

7.  Is  its  "nut"  a  root  or  a  tuber?     How  can  you  tell?     (106.) 

8.  Suggest  some  ways  for  destroying  weeds  that  are  propagated  in  this 
way. 

9.  Could  you  get  rid  of  wild  onions  in  a  pasture  by  mowing  them  down  ? 
By  digging  them  up  ?     (107.) 

10.  Is  it  wise  for  farmers  to  neglect  the  appearance  of  such  a  weed 
in  their  neighborhood,  even  though  it  does  not  infest  their  own  land  ? 

11.  Name  any  plants  of  your  neighborhood,  either  wild  or  cultivated, 
that  are  valued  for  their  rhizomes ;  for  their  tubers. 

12.  What  part  of  the  plants  named  below  do  we  use  for  food  or  other 
purposes?  Ginger,  angelica,  ginseng,  cassava,  arrowroot,  garlic,  onion, 
sweet  flag,  iris,  sweet  potato,  Cuba  yam,  artichoke. 

13.  Wliy  are  the  true  roots  of  bulbous  and  rhizome-bearing  plants 
generally  so  much  smaller  in  proportion  to  the  other  parts  than  those  of 
ordinary  plants  ?     (89,104.) 

14.  If  the  Canada  thistle  grows  in  your  vicinity,  examine  the  roots  and 
see  if  there  is  anything  about  them  that  will  help  to  account  for  its  hardi- 
hood and  persistency. 

15.  If  you  live  in  the  region  of  the  horse  nettle  (Solamim  Carolinense), 
explain  how  it  is  helped  by  its  root  system.     (89.) 


96  PRACTICAL  COURSE  IN  BOTANY 

m.  STEM  STRUCTURE 

A.     MONOCOTYLS 

Material.  —  Fresh  cornstalks  with  several  well-  developed  nodes, 
some  of  which  should  have  stood  in  coloring  fluid  from  1  to  3  hours.  If 
fresh  specimens  cannot  be  obtained  from  the  fields,  a  number  of  seedlings 
maj^  be  grown  in  boxes  of  rich  earth  and  cared  for  by  the  pupils  either  at 
home  or  in  the  schoolroom ;  they  should  be  planted  4  or  5  weeks  before 
needed.  Asparagus  and  smilax  sprouts  may  be  used,  or  the  stem  of  any 
large  grass,  or  of  wheat  and  other  grains,  but  stalks  of  corn  or  sugar  cane 
make  the  best  subjects  for  study  where  they  can  be  obtained. 

Appliances.  —  A  compound  microscope  will  be  needed  for  detailed 
study.  Prepared  slides  can  be  used,  but  it  is  better  for  students  to  make 
their  own  sections  where  practicable. 

1 10.   Gross   anatomy  of  a  monocotyl  stem.  —  Obtain  a 

fresh  cornstalk,  —  preferably  one  that  has  begun  to  tassel,  — 

and  observe  its  external  characters.     How  are  the  inter- 

p  nodes  divided  from  one  another  ?     What 

^    ..1/    is  the  use  of  the  very  firm,  smooth  epider- 

>-''         mis  ?     Notice  a  hollow,  grooved   channel 

running  down  one  side  between  the  joints, 

or  nodes  ;  does  it  occur  in  all  of  them  ? 

Fig.  112.— Cross    Is  it  ou  the  samo  side  or  on  the  opposite 

TT,o  if.  I  TZT't^    sides  of  alternate  internodes  ?     Follow  one 

(reduced)  :  v,  nbro-vas- 

cuiar  bundles ;  c,  cor-  of  theso  groovcs  to  the  nodo  from  which 
^^ '  ^'^^   '  it  originates  ;    what  do  you   find   there  ? 

After  studying  the  internal  structure  of  the  stalk,  you  will 
understand  why  this  groove  should  occur  on  the  side  of  an 
internode  bearing  a  bud  or  fruit. 

Cut  a  cross  section  midway  between  two  nodes,  and  ob- 
serve the  composition  of  the  interior ;  of  what  does  the  bulk 
of  it  appear  to  consist?  Notice  the  arrangement  of  the 
little  (lots,  like  the  ends  of  cut-off  threads,  that  are  scattered 
through  the  pith  ;  where  are  they  most  abundant,  toward  the 
center  or  the  circumference  ? 

Make  a  vertical  section  through  one  of  the  nodes.  Cut  a 
thin  slice  of  the  pith,  hold  it  up  to  the  light,  and  examine 


THE  STEM 


97 


Fig.  113.  — Ver- 
tical section  of  corn- 
stalk (reduced)  :  g, 
groove  ;  c,  cortex  ;  v, 
fibrovascular  bundles 
mingled  with  paren- 
chyma ;  h,  bud ;  n, 
node. 


with  a  hand  lens.  Observe  that  it  is  composed  of  a  number 
of  oblong  cells  packed  together  like  bricks  in  a  wall.  These 
are  filled  with  protoplasm  and  cell  sap,  and  constitute  what  is 
known  to  botanists  as  the  parenchyma  or 
fundamental  tissue  from  which  all  the  other 
tissues  are  derived.  Apply  the  iodine  test ; 
in  what  parts  does  starch  occur  most  abun- 
dantly ? 

Draw  out  one  of  the  woody  threads  run- 
ning through  the  pith.  Break  away  a  bit  of 
the  epidermis,  and  see  how  very  closely  they 
are  packed  on  its  inner  surface.  Trace  the 
course  of  the  veins  in  the  bases  of  the  leaves ; 
find  their  point  of  union  with  the  stem; 
with  what  part  of  it  do  they  appear  to  be 
continuous  ?  Has  this  anything  to  do  with 
the  greater  abundance  of  fibers  near  the  epi- 
dermis ?  Can  you  follow  the  fibers  through 
the  nodes,  or  do  they  become  confused  and  intermixed  with 
other  threads  there?  (If  a  stalk  of  sugar  cane  can  be 
obtained,  the  ring  of  scars  left  by  the  vascular  bundles  as 
they  pass  from  the  leaves  into  the  stem  will  be  seen  beauti- 
fully marked  just  above  the  nodes.) 

If  there  is  an  eye  or  bud  at  the  node,  see  if  any  of 
the  threads  go  into  it.  Can  you  account  now  for  the  de- 
pression that  occurs  in  the  internode  above  the  eye? 

Make  drawings  of  both  cross  and  vertical  sections,  showing 
the  points  brought  out  in  your  examination  of  the  cornstalk. 

III.  The  vascular  system.  —  To  find  out  the  use  of  the 
threads  that  you  have  been  tracing,  examine  a  piece  of  a 
living  stem  that  has  stood  in  red  ink  for  three  to  twenty-four 
hours.  Notice  the  course  the  coloring  fluid  has  taken ;  what 
would  you  infer  from  this  as  to  the  use  of  the  woody  fibers  ? 

These  threads  constitute  what  is  called  the  vascular  system 
of  the  stem,  because  they  are  made  up  of  vessels  or  ducts, 
along  which  the  sap  is  conveyed  from  the  roots  to  the  leaves 


98 


PRACTICAL  COURSE  IN  BOTANY 


and  back  from  the  leaves  to  the  parts  where  it  is  needed  after 
it  has  contributed  to  the  elaboration  of  food. 

On  account  of  this  double  line  of  communication  which 
they  have  to  maintain,  the  vascular  threads,  or  bundles,  as 
they  are  technically  called,  are  double ;  one  part  composed 
of  larger  vessels,  carrying  water  up,  the  other  consisting  of 
smaller  ones,  bringing  back  the  food.  Can  you  give  a  reason 
for  their  difference  in  size  ? 

112.  Woody  monocotyls.  —  Examine  sections  of  yucca, 
smilax,  or  of  palmetto  from  the  handle  of  a  fan,  and  compare 
them  with  your  sketches  of  the  cornstalk. 
In  which  are  the  vascular  fibers  most  abun- 
dant? Which  is  the  toughest  and  strongest? 
Why?  Trace  the  course  of  the  leaf  fibers 
from  the  point  of  insertion  to  the  interior. 
How  does  it  differ  from  that  of  the  fibers 
in  a  cornstalk  ? 

1 13 .  Growth  of  monocotyl  stems.  —  After 
tracing  the  course  of  the  leaf  veins  at  the 
nodes  of  the  cornstalk,  you  will  have  no 
difficulty  in  identifying  these  veins  as  part  of 
the  vascular  system.  In  jointed  stems  like 
those  of  the  corn  and  sugar  cane  and  other 
grasses,  their  intercalation  between  the  vas- 
cular bundles  of  the  stem  takes  place,  as  we 
have  seen,  at  the  nodes,  forming  the  hard 
rings  known  as  joints;  but  in  other  mono- 
cotyls the  fibers  entering  the  stem  from  the 
leaves  usually  tend  first  downward,  toward  the  interior 
(Fig.  114),  then  bend  outward,  toward  the  surface,  where  they 
become  entwined  with  others  and  form  the  tough,  inseparable 
cortex  that  gives  to  palmetto  and  bamboo  stems  their  great 
strength.  Generally,  monocotyl  stems  do  not  increase  in  di- 
ameter after  a  certain  point,  and  as  they  can  contain  only  a 
limited  number  of  vascular  fibers,  they  are  incapable  of  sup- 
porting an  extended  system  of  leaves  and  branches.     Hence 


Fig.  114.  — Lon- 
gitudinal section 
through  the  stem 
of  a  palm,  showing 
the  curved  course  of 
the  fibrovascular 
bundles  (Gray,  after 
Falkenberg). 


THE  STEM 


Plate  4. — Forest  of  bamboo,  showiii'j-  i  In   i  .11 
iuonocot>  1  aicuib. 


lu;,iirl,|,.-,  Irililt    ,,| 


100 


PRACTICAL  COURSE  IN  BOTANY 


plants  of  this  class,  with  a  few  exceptions,  like  smilax  and 
asparagus,  are  characterized  by  simple,  columnar  stems  and 
a  limited  spread  of  leaves.  Such  plant  forms  are  admirably- 
adapted  by  their  structure  to  the  purposes  of  mechanical 
support.  It  is  a  well-known  law  of  mechanics  that  a  hollow 
cylinder  is  a  great  deal  stronger  than  the  same  mass  would 
be  in  solid  form,  as  may  easily  be  tested  by  the  simple  ex- 
periment of  breaking  in  your  fingers  a  cedar  pencil  and  a 
joint  of  cane  or  a  stem  of  smilax  of  the  same  weight.  In 
stems  that  may  be  technically  classed  as  solid  in  structure, 
like  the  corn  and  palmetto,  the  interior  is  so  light  compared 
with  the  hard  epidermis  that  the  result  is  practically  a  hollow 
cylinder. 

114.   Minute  study  of  a  monocotyl  stem.  —  Place  under 
the  microscope  a  very  thin  transverse  section  of  a  cornstalk. 

The  little  dots  that  looked  like 
^  the  cut  ends  of  threads  to  the 

^  naked  eye  will  now  appear  as 

5Px  y  ^^  ^p      '3 


Fig.  115.— Transverse  section  through 
the  fibrovascular  bundle  of  a  cornstalk  : 


Fig.  116.  —  Vertical  section  of  the  same  ; 


a,  annular  trachcid  ;  sp,  spiral  tracheid  ;    a  and  a',  rings  of  a  decomposed   annular 


ni  and  m',  ducts  ;  /,  air  space  ;  v,  sieve 
tubes  ;  n,  companion  cells  ;  vg,  strength- 
ening fibers  ;  cp,  bast ;  /,  /,  parenchyma. 


trachcid ;  v,  sieve  tubes ;  s,  companion 
cells  ;  cp,  bast ;  /,  air  space  ;  vg,  strength- 
ening tissue  ;  sp,  spiral  duct. 


the  complex  group  of  cells  shown  in  Fig.  115.    The  same  parts 
are  shown  longitudinally  in  Fig.  116.    As  seen  in  cross  sec- 


THE   STEM  101 

tion,  their  arrangement  suggests  a  grotesque  resemblance  to 
the  face  of  an  old  woman  wearing  a  pair  of  enormous  specta- 
cles and  surrounded  by  a  cap  frill  of  netting  with  very  wide 
meshes.  These  are  parenchyma  cells,  /,  /,  Fig.  115,  and 
constitute  the  greater  portion  of  the  living  tissues. 

The  two  large  openings,  m,  m! ,  that  represent  the  spectacles, 
are  ducts  for  carrying  water  up  the  stem.  They  are  called 
pitted  ducts  on  account  of  the  bordered  pits  which  cover 
their  outer  surface.  The  two  smaller  openings  between  and 
slightly  below  the  pitted  ducts  are  also  vessels  for  carrying 
liquids  up  the  stem.  The  lower  one,  a,  is  called  the  annular 
tracheid  because  its  tube  is  strengthened  by  rings  on  the 
inside.  The  upper,  smaller  one,  sp,  is  known  as  the  spiral 
tracheid,  because  its  walls  are  reinforced  by  spiral  thickenings. 
Can  you  think  what  is  the  use  of  these  strengthening  contri- 
vances in  the  walls  of  conducting  cells?  (Suggestion:  What 
is  the  use  of  the  spiral  wire  on  a  garden  hose?)  The  large, 
irregular  opening  below  the  ducts  is  an  air  space.  What  is 
its  object?     Why  has  it  no  surrounding  wall? 

Next  look  above  the  ducts  for  a  group  of  rhomboidal  or 
hexagonal  cells,  v,  v,  with  smaller  ones,  s,  between  them.  The 
larger  of  these  are  sieve  tubes,  the  smaller 
ones,  co7npanion  cells.  The  sieve  tubes 
carry  sap  down  the  stem  after  it  has  been 
made  into  food  by  the  leaves.  They  get 
their  name  from  the  sievelike  openings 
between  the  connecting  walls  of  the  cells 
which  form  them  —  as  if  a  row  of  pepper 
boxes  with  perforations  at  both  top  and      ,^J".-  ly  —  Honzon- 

^  tal  view  of  the  sieve  tube 

bottom  were  placed  end  to  end,  so  as  to  of  a  gourd  stem,  showing 
form  a  long  tube  divided  into  compart-  Perforations. 
ments  by  perforated  walls.  Can  you  give  a  reason  why  the 
cells  of  ducts  that  carry  elaborated  nutriment  should  have  a 
more  open  line  of  communication  than  those  carrjdng  crude 
sap  ?  [56  (2) .]  Which  one  of  the  organic  food  substances  was 
shown  by  Exp.  39  to  be  unable,  or  nearly  so,  to  pass  through 


102 


PRACTICAL  COURSE  IN  BOTANY 


r       u 

Fig.  118.— Side 
view  of  the  sieve 
tube  of  a  gourd  stem  : 
pr,  protoplasm  layer ; 
u,  albuminous  con- 
tents, forming  muci- 
laginous strand. 


the  cell  wall  by  osmosis?  [56  (4).]  The 
conducting  cells  are  surrounded  by  a  mass 
of  strengthening  fibers  separating  them 
from  the  parenchyma,/,  and  constituting 
with  them  a  fibrovascular  bundle.  The 
larger  vessels,  m,  m' ,  a,  and  sjj,  compose 
the  xylem,  the  harder,  more  woody  part 
of  the  bundle,  and  the  smaller  ones,  v,  s, 
the  phloem,  or  softer  part.  Notice  also 
that  there  is  no  parenchyma  in  contact 
with  the  xylem  and  phloem  in  the  fibro- 
vascular bundles  of  a  monocotyl,  to  supply 
material  for  new  growth,  but  they  are 
entirely  surrounded  by  a  sheath  of  strength- 
ening tissue,  whence  such  bundles  are  said 
to  be  closed,  and  are  incapable  of  further 
growth  by  the  addition  of  new  cells. 

B.   Herbaceous  Dicotyls 


Material.  —  Young  stems  of  sunflower,  hollyhock,  burdock,  ragweed, 
cocklebur,  castor  bean,  or  any  large  herbaceous  plant.  In  schools  un- 
provided with  compound  microscopes,  the  minute  anatomy  can  be  studied 
with  some  degree  of  profit  by  the  aid  of  pictures. 

115.  Gross  anatomy.  —  Examine  the  outside  of  a  young 
stem  of  sunflower,  burdock,  or  other  herbaceous  dicotyl. 
Notice  whether  it  is  smooth,  or  roughened  with  hairs,  scales, 
ridges,  or  grooves.  If  hairy,  observe  the  nature  of  the  hairs, 
whether  bristly,  downy,  sticky,  etc.  Notice  the  color  of  the 
epidermis,  whether  uniform,  or  splotched  or  striped  with 
other  colors,  as,  for  example,  jimson  weed,  and  pigweed 
(amarantus).  If  there  are  any  buds,  branches,  or  flower 
stems,  notice  where  they  originate ;  what  is  the  angle  be- 
tween the  leaf  and  stem  called?     (100.) 

Make  a  transverse  cut  through  a  portion  of  the  stem  that 
has  stood  for  a  time  in  coloring  fluid  and  examine  with  a  lens. 
Four  regions  can  easily  be  distinguished  :  (1)  the  epidermis, 


THE  STEM 


103 


Fig.  119.  —  'riaiisvcrso  section  of  a 
very  young  stem  of  burdock,  showing  fibro- 
vascular  bundles  not  completely  united 
into  a  ring  :  e,  epidermis  ;  c,  primary  cor- 
tex ;  /,  a  ring  of  fibrovascular  bundles ; 
p,  central  cylinder  of  parenchyma. 


e,  Fig.  119;  (2)  the  primary  cortex,  c;  (3)  a  ring  of  fibro- 
vascular bundles,  /;  and  (4)  a  central  cylinder  of  paren- 
chyma, p.  In  some  specimens  there  will  be  a  fifth  region,  the 
pith,  which  will  appear  in 
the  section  as  a  white  cir- 
cular spot  in  the  center  of 
the  parenchyma. 

In  specimens  a  little  older 
than  the  one  shown  in  Fig. 
119,  a  narrow  circular  line 
will  be  seen  running  through 
the  ring  of  bundles  nearly 
midway  between  their  inner 
and  outer  extremities,  con- 
necting them  into  an  un- 
broken circle  around  the 
central  cylinder.  This  is 
the  camhiu7n  layer,  which  supplies  the  vascular  region  with 
materials  for  new  growth,  and  thus  enables  dicotyl  stems  to 
increase  in  diameter  by  the  successive  addition  of  fresh 
vascular  rings  from  year  to  year. 

Examine  in  the  same  way  a  vertical  section,  and  find  the 
parts  corresponding  to  those  shown  in  Fig.  119.  Make  en- 
larged sketches  of  both  sections,  labeling  the  various  parts 
observed. 

ii6.  Minute  structure  of  a  dicotyl  stem.  —  Place  suc- 
cessively under  a  high  power  of  the  microscope  thin  trans- 
verse and  longitudinal  sections  of  the  stem  just  examined,  or 
such  other  specimen  as  the  teacher  may  provide.  Bring  one 
of  the  fibrovascular  bundles  into  the  field,  and  try  to  make 
out  the  parts  shown  in  Figs.  120  and  121.  The  corresponding 
parts  in  the  two  sections  are  indicated  by  the  same  letters. 
Notice  the  cortex,  R,  on  the  outside  and  the  pith,  M,  on  the 
inside  ;  between  these,  the  cambium,  C,  the  xylem,  or  woody 
tissue,  included  between  the  radiating  lines  X,  and  the  newer 
tissues  composing   the  phloem  between  the  lines  P.     The 


104 


PRACTICAL  COURSE  IN  BOTANY 


C    sb  ,    h  P 


121 


R 


-A 


Figs.  120-121.  —  Transverse  and  longitudinal  sections  of  a  fibrovasoular  bundle 
in  the  stem  of  a  sunflower.  The  two  sections  are  lettered  to  correspond  :  M,  pith 
(parenchyma)  ;  X,  xylcm  region  ;  P,  phloem  ;  R,  cortex  ;  s,  spiral  ducts  ;  s',  annular 
ducts:  t,t,  pitted  ducts;  C,  cambium  between  the  phloem  and  xylem  regions;  sb, 
sieve  tubes;  6,  bast;  e,  bundle  sheath;  ic,  cambium  (parenchyma)  cells;  h,  wood  fioers. 


THE  STEM  105 

cambium  and  pith,  which  includes  the  medullary  rays  so  con- 
spicuous in  perennial  stems,  are  composed  of  live  paren- 
chyma cells,  from  which  alone  growth  can  take  place ;  they 
are  the  active  part  of  the  stem.  The  xylem  contains  the 
large  vessels,  t  and  s,  that  convey  water  up  the  stem,  together 
with  the  wood  fibers,  h.  These  are  the  permanent  tissues. 
After  completing  their  growth  the  cells  of  the  xylem  gradu- 
ally lose  their  protoplasm,  and  all  vitality  ceases.  Even  the 
cell  sap  disappears,  and  sometimes  the  walls  of  the  ducts  are 
disintegrated,  leaving  a  mere  air  space  like  that  shown  at  I  in 
Figs.  115  and  116.  The  dead  cells  and  tissues,  however,  are 
by  no  means  useless.  They  constitute  the  heartwood  that 
is  so  valuable  for  timber,  and  serve  an  important  purpose  as 
a  mechanical  support  for  the  stem.  The  phloem  contains 
on  its  outer  face  a  mass  of  hard  fibers,  h,  called  bast,  and 
toward  the  interior,  the  sieve  tubes,  sb,  with  a  number  of 
smaller  vessels  that  convey  down  the  stem  the  sap  containing 
the  food  made  in  the  leaves.  It  is  separated  from  the  cortex 
by  the  bundle  sheath,  e,  and  on  its  other  side,  from  the  ex- 
terior face  of  the  xylem  by  the  cambium,  C.  In  this  position 
the  growing  cambium  adds  new  cells  to  the  inner  side  of  the 
phloem,  and  to  the  outer  side  of  the  xylem,  so  that  the  former 
grows  on  its  inner  face  and  the  latter  on  its  outer.  In  peren- 
nial plants,  as  new  rings  are  added  to  the  xylem  from  season 
to  season,  the  older  anes  die  and  are  changed  into  heartwood, 
which  thus  gradually  increases  in  thickness  till  in  some  of  the 
giant  redwoods  and  eucalypti,  it  may  attain  a  diameter  of 
thirty-five  or  forty  feet.  In  the  phloem,  on  the  other  hand, 
as  new  cells  are  added  from  within,  the  older  ones  are 
gradually  changed  into  hard  bast,  h,  then  into  bark,  and 
are  finally  sloughed  off  and  fall  to  the  ground.  It  is  this 
free  line  of  communication  with  the  active  cambium  that 
enables  dicotyl  stems  to  grow  on  indefinitely,  the  sheath,  e, 
being  formed  on  the  exterior  face  of  the  bundles  only,  leav- 
ing the  other  free,  whence  they  are  said  to  be  open. 
Make  drawings  of  cross  and  vertical  sections  of  a  dicotyl 


106 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  122.  —  Internal  structure  of  a  pine  stem,  showing  longitudinal  section  of  a 
fibrovascular  bundle  through  a  medullary  ray,  sm,  sm'  :  s,  tracheids;  t,  bordered 
pits,  surface  view;  c,  cambium;  v,  sieve  tubes;  vt,  sieve  pits,  analogous  to  the 
sieve  plates  in  dicotyl  stems. 

stem  as  it  appears  under  the  microscope,  labeling  correctly 
all  the  parts  observed.     Show  the  shape  and  relative  size  of 

the  different  cells.  Com- 
pare your  drawings  with 
those  made  in  your  study 
of  monocotyl  stems,  and 
write  in  your  notebook  the 
essential  points  of  difference 
between  the  two. 

117.  The  stems  of  coni- 
fers, the  group  of  Gymno- 
sperms  to  which  the  pine 
belongs,  do  not  differ  greatly 
from  those  of  dicotyls,  the 
chief  difference  being  that 
the  vascular  bundles  contain 
tracheids  only,  correspond- 
ing to  the  smaller  vessels  of 


Fi(!.  Ti.i. —  Intcrnalstructureof  a  pine 
stem,  showing  transverse  section  of  a  tra- 
cheid  :  7,  cell  walls;  //),  intermediate  layer 
between  walls  of  adjoining  cells ;  m',  inter- 
cellular space  here  occupied  by  substance 
of  intermediate  layer;  b,  bordered  pit  in 
section  at  right  angles  to  the  surface ;  t, 
membrane  for  closing  the  pit  canal. 


THE  STEM 


107 


the  phloem,  s  and  s',  shown  in  Fig.  121.  These  tracheids 
have  large  sunken  places  in  their  walls,  called  bordered  pits 
(Fig.  123),  closed  by  a  very  thin  membrane  through  which 
water  and  dissolved  food  materials  can  mon^  I'eadily  per- 
colate. In  all  other  essentials,  the  internal  structure  of  pine 
stems  is  like  that  of  dicotyls.     (See  Plate  5.) 

C.  Woody  Stemmed  Dicotyl 

Material.  —  Elm,  basswood,  mulberry,  leatherwood,  and  pawpaw 
show  the  bast  well ;  sassafras,  slippery  elm,  and  (in  spring)  hickory  and 
willow  show  the  cambiimi;  grape  and  trumpet  vine,  the  ducts.  Some 
of  the  specimens  used  should  be  placed  in  coloring  fluid  from  3  to  8  hours 
before  the  lesson  begins.  The  rate  at  which  the  liquid  is  absorbed  varies 
with  the  kind  of  stem  and  the  season.  It  is  more  rapid  in  spring  and  slower 
in  winter.  If  a  cutting  stands  too  long  in  the  fluid,  the  dye  will  gradually 
percolate  through  all  parts  of  it ;  care  should  be  taken  to  guard  against  this, 

ii8.  The  external  layer.  —  While  the  primary  structures, 
as  shown  in  the  last  section,  are  essentially  the  same  in  all 
dicotyl  stems,  the  continued  yearly 
growth  of  perennials  causes  them  to  de- 
velop a  number  of  secondary  structures 
and  variations  of  detail  that  differentiate 
them  in  a  marked  degree  from  soft- 
stemmed  annuals.  Take  a  piece  of  a 
three-year-old  shoot  of  cherry,  horse 
chestnut,  or  any  convenient  hardwood 
tree,  and  notice  that  the  soft,  green 
epidermis  has  given  place  to  a  thicker, 
harder,  and  usually  darker  colored  bark. 
Notice  the  presence  of  lenticels  (106)  and 
their  porous,  corky  texture  for  the  ad- 
mission of  air  to  the  interior.  They 
are  slightly  raised  above  the  surface  of 
the  bark,  and  are  usually  round,  or 
more  or  less  elongated  in  different  direc- 
tions, according  as  they  are  stretched 
zontally  by  the  growth  of  the  axis. 


Fig.  124.  — Part  of  a 
young  China  tree  shoot, 
showing,  A,  lenticels;  B, 
leaf  scar ;  C,  C,  traces  left 
by  the  broken  ends  of 
fibrovascular  bundles  that 
passed  from  the  stem  in- 
to the  leaf.    Natural  size. 

vertically  or  hori- 
The  characteristic  mark- 


108 


PRACTICAL  COURSE   IN   BOTANY 


Plate  5.  —  Stem  of  a  conifer,  Sequoia  gigantea,  Mariposa  Grove,  California  The 
first  branch,  6  feet  in  diameter,  leaves  the  parent  trunk  125  feet  above  the  ground. 
The  photographer  sitting  on  one  of  the  exposed  roots  affords  a  good  standard  for 
comparison.  The  tree  is  noted  for  its  massive  limbs.  The  smaller  trees  in  the 
background  show  the  characteristic  mode  of  branching  in  trees  of  this  class. 


THE  STEM  109 

ings  of  birch  bark,  which  make  it  so  ornamental,  are  due  to  the 
lenticels.  In  most  trees  they  disappear  on  the  older  parts, 
where  the  bark  is  constantly  breaking  away  and  sloughing  off. 

up.  Internal  structures.  —  Cut  a  transverse  section 
through  your  specimen,  and  notice  under  the  epidermis  a 
greenish  layer  of  young  bark ;  beneath  this  a  layer  of  rather 
tough,  stringy  bast  fibers,  and  beyond  these  a  harder  woody 
substance  that  constitutes  the  bulk  of  the  interior;  within  this, 
at  the  very  center  of  the  axis,  we  find  a  cylinder  of  lighter 
texture,  the  pith,  or  medulla,  occupying  the  place  of  the  soft 
parenchyma  which  fills  this  space  in  very  young  stems. 

Between  the  woody  axis  and  the  bark  notice  a  more  or 
less  soft  and  juicy  ring. 

120.  The  cambium  layer.  —  This  is  not  always  easily 
distinguishable  with  a  hand  lens,  but  is  conspicuous  in  the 
stems  of  sassafras,  slippery  elm,  and  aristolochia.  If  some 
of  these  cannot  be  obtained,  the  presence  of  the  cambium 
can  be  recognized  by  observing  the  tendency  of  most  stems 
to  "  bleed,"  when  cut,  between  the  wood  and  bark.  The 
reason  for  this  is  because  the  cambium  is  the  active  part  of 
the  stem,  in  which  growth  is  taking  place,  and  consequently 
it  is  most  abundantly  supplied  with  sap.  In  spring,  es- 
pecially, it  becomes  so  full  of  sap  that  if  a  rod  of  hickory 
or  elder  is  pounded,  the  pulpy  cambium  is  broken  up  and  the 
bark  may  be  slipped  off  whole  from  the  wood. 

121.  Medullary  rays.  —  Observe  the  whitish,  silvery  lines 
that  radiate  in  every  direction  from  the  center,  like  the 
spokes  of  a  wheel  from  the  hub.  These  are  the  medullary 
rays,  and  consist  of  threads  of  pith  that  serve  as  lines  of  com- 
munication between  the  "  central  cylinder  "  and  the  grow- 
ing cambium  layer.  In  old  stems  the  central  pith  frequently 
disappears  and  its  office  is  filled  by  the  medullary  rays,  which 
become  quite  conspicuous. 

122.  Structural  regions  of  a  woody  stem.  —  Sketch  cross 
and  vertical  sections  of  your  specimen,  as  seen  under  the  lens, 
labeling  the  different  parts.    Refer  to  Figs.  125,  126,  if  you 


110 


PRACTICAL  COURSE  EST  BOTANY 


have  any  difficulty  in  distinguishing  the  parts.  In  a  year-old 
shoot  (Fig.  125),  the  structural  regions  correspond  closely  to 
those  shown  in  Fig.  119,  except  that  the  ring  of  fibrovascular 
bundles  is  here  compact  and  woody,  and  crossed  by  the 
radiating  lines  of  the  medullary  rays.  In  a  three-year-old 
shoot  (Fig.  126),  the  main  divisions  are  the  same,  but  the 
soft  parenchyma  of  the  central  cylinder  is  replaced  by  the 
pith,  and  the  vascular  ring  is  composed  of  three  layers  corre- 
sponding to  the  three  years  of  growth.      In  general,  mature 


125  126 

Figs.  125,  126.  — Cross  sections  of  twigs  :  125,  section  across  a  young  twig  of  box 
elder,  showing  the  four  stem  regions  :  e,  epidermis,  represented  by  the  heavy  bounding 
line  ;  c,  cortex  ;  w,  vascular  cylinder  ;  p,  pith  ;  126,  section  across  a  twig  of  box  elder 
three  years  old,  showing  three  annual  growth  rings,  in  the  vascular  cylinder.  The 
radiating  lines  (m),  which  cross  the  vascular  region  (w),  represent  the  pith  rays,  the 
principal  ones  extending  from  the  pith  to  the  cortex  (c).  (From  Coulter's  "  Plant 
Relations.") 


dicotyl  stems  may  be  said  to  include  four  well-defined  re- 
gions: (1)  the  epidermis,  or  the  bark;  (2)  the  cortex,  made 
up  of  bast  and  certain  other  tis.sues;  (3)  the  cambium; 
(4)  the  woody  vascular  cylinder,  made  up  of  concentric 
rings,  each  representing  a  year's  growth.  The  pith,  or  me- 
dulla, constitutes  a  fifth  region,  but  is  obvious  only  in  young 
stems.  Notice  the  little  pores  or  cavities  that  dot  the  woody 
part  in  the  cross  section ;  where  are  they  largest  and  most 
abundant  ?    How  are  the  rings  marked  off  from  one  another  ? 


THE  STEM 


111 


These  pores  are  the  sections  of  ducts.  They  are  very  large 
in  the  grapevine,  and  a  cutting  two  or  three  years  old  will 
show  them  distinctly.  Examine  sections  of  a  twig  that  has 
stood  in  red  ink  from  three  to  twelve  hours,  and  observe  the 
course  the  fluid  has  taken.  How  does  this  accord  with  the 
facts  observed  in  your  study  of  the  conducting  tissues  in 
monocotyl  and  herbaceous  stems?     (Ill,  115,  116.) 

123.  The  rings  into  which  the  woody  cylinder  is  divided 
mark  the  yearly  additions  to  the  growth  of  the  stem,  which 
increases  by  the  constant  accession  of  new 
material  to  the  outside  of  the  permanent 
tissues  (116).  The  cambium  constantly 
advances  outward,  beginning  every  spring 
a  new  season's  growth,  and  leaving  behind 
the  ring  of  ducts  and  woody  fibers  made 
the  year  before.  As  the  work  of  the  plant  is 
most  active  and  its  growth  most  vigorous 
in  spring,  the  largest  ducts  are  formed  then, 
the  tissue  becoming  closer  and  finer  as  the 
season  advances,  thus  causing  the  division 
into  annual  rings  that  is  so  characteristic  of 
woody  dicotyl  stems.  Each  new  stratum  of 
growth  is  made  up  of  the  fibrovascular 
bundles  that  supply  the  leaves  and  buds  and 
branches  of  the  season.  In  this  way  we  see 
that  the  increase  of  dicotyl  trunks  and 
branches  is  approximately  in  an  elongated 
cone  (Fig.  127),  the  number  of  rings  gradually  diminishing 
toward  the  top  till  at  the  terminal  bud  of  each  bough  it  is 
reduced  to  a  single  one,  as  in  the  stems  of  annuals. 

Sometimes  a  late  autumn,  succeeding  a  very  dry  summer, 
will  cause  trees  to  take  on  a  second  growth,  and  thus  form  two 
layers  of  wood  in  a  single  season.  On  this  account  we  can- 
not always  rely  absolutely  upon  the  number  of  rings  in  esti- 
mating the  age  of  a  tree,  though  the  method  is  sufficiently 
exact  for  all  practical  purposes. 


Fig.  127.  — Dia- 
gram illustrating  the 
annual  growth  of 
dicotyledons. 


112  PRACTICAL  COURSE  IN  BOTANY 


Practical  Questions 

1.  Old  Fort  Moultrie  near  Charleston  was  built  originally  of  palmetto 
logs;   was  this  good  engineering  or  not ?     Why?     (113.) 

2.  Explain  the  advantages  of  structure  in  a  culm  of  wheat ;  a  stalk  of 
corn;  arced.     (113.) 

3.  Would  the  same  quality  be  of  advantage  to  an  oak  ?     Why,  or  why 
not? 

4.  Is  it  of  any  advantage  to  the  farmer  that  grain  straw  is  so  light  ? 

5.  Explain  why  boys  can  slip  the  bark  from  certain  kinds  of  wood  in 
spring  to  make  whistles.     (120.) 

6.  Why  cannot  they  do  this  in  autumn  or  winter?     (123.) 

7.  Name  some  of  the  plants  commonly  used  for  this  purpose. 

8.  Is  the  spring,  after  the  buds  begin  to  swell,  a  good  time  to  prune 
fruit  trees  and  hedges  ?     (120.) 

9.  What  is  the  best  time,  and  why? 

10.  Why  are  grapevines  liable  to  bleed  to  death  if  pruned  too  late  in 
spring?     (120,  123.) 

11.  Wliy  are  nurserymen,  in  grafting,  so  careful  to  make  the  cambium 
layer  of  the  graft  hit  that  of  the  stock?     (120.) 

12.  In  calculating  the  age  of  a  tree  or  bough  from  the  rings  of  annual 
growth,  should  we  take  a  section  from  near  the  tip,  or  from  the  base  ? 
Why?     (123.) 

IV.    THE   WORK    OF    STEMS 

Material.  —  Leafy  shoots  of  grape,  balsam,  peach,  or  other  active 
young  stems ;  a  cutting  of  willow,  currant,  or  any  kind  of  easily  rooting 
stem.     Two  bottles  of  water  and  some  linseed  or  cottonseed  oil. 

Experiment  58.  Do  the  leaves  have  any  active  part  in  effecting 
THE  movement  OF  SAP  IN  THE  STEM  ?  —  Take  two  healthy  young  shoots  of 
the  same  kind  —  grape,  peach,  corn,  tropaolum,  calla  lily  absorb  rapidly. 
Trim  the  leaves  from  one  shoot  and  close  the  cut  surfaces  with  a  little  vase- 
line or  gardener's  wax  to  prevent  loss  of  water  by  evaporation.  Place  the 
lower  end  of  each  in  a  glass  jar  or  tumbler  filled  to  the  same  height  with 
water.  Cut  off  under  loater  a  half  inch  from  the  bottom  of  each  shoot, 
to  get  a  fresh  absorbing  surface.  This  is  necessary  because  exposure  to 
air  for  even  a  second  greatly  hinders  absorption  by  permitting  the  entrance 
of  air  into  the  severed  ends  of  the  ducts.  Pour  a  little  oil  on  the  water  in 
both  jars  to  prevent  evaporation.  (Do  not  use  kerosene  ;  it  is  injurious 
to  plants.)  At  the  end  of  twenty-four  hours,  which  vessel  has  lost  the 
more  water  ?    How  do  you  account  for  the  difference  ? 


THE  STEM 


113 


Experiment  59.  What  becomes  of  the  water  that  goes  into  the 
LEAVES  ?  —  Cover  the  top  of  the  vessel  containing  the  leafy  twig  used  in  the 
last  experiment  with  a  piece  of  card- 
board, having  first  cut  a  slit  in  one  side, 
as  shown  in  Fig.  128,  so  that  it  can  be 
slid  into  place  without  injuring  the 
stem.  Invert  over  the  twig  a  tumbler 
that  has  first  been  thoroughly  dried, 
and  leave  in  a  warm,  dry  place.  After 
an  hour  or  two,  what  do  you  see  on  the 
inside  of  the  tumbler  ?  Where  did  the 
moisture  come  from  ? 

Experiment  60.     Through   what 

PART  of  the  stem  DOES  THE  SAP  FLOW 

UPWARD  ?  —  Remove  a  ring  of  the  cor- 
tical layer  from  a 
twig  of  any  readily 
rooting  dicoty], 
such  as  willow, 
being  careful  to 
leave     the    woody 

part,  with  the  cambium,  intact.  Place  the  end  beloio 
the  cut  ring  in  water,  as  shown  in  Fig.  129.  The  leaves 
above  the  girdle  will  remain  fresh.  How  is  the  water 
carried  to  them?  How  does  this  agree  with  the 
movement  of  red  ink  observed  in  115  and  122? 

Experiment  61.  Through  what  part  does  the 
SAP  COME  DOWN  ?  —  Ncxt  pruue  away  the  leaves  and 
protect  the  girdled  surface  with  tin  foil,  or  insert  it 
below  the  neck  of  a  deep  bottle  to  prevent  evaporation, 
and  wait  until  roots  develop.  Do  they  come  more 
abundantly  from  above  or  below  the  decorticated 
ring? 


Fig.  128.  —  Experiment  showing 
that  moisture  is  thrown  off  by  the 
leaves  of  plants. 


Fig.  129.  —a 
twig  which  had  been 
kept  standing  in 
water  after  the  re- 
moval of  a  ring  of 
cottical  tissue :  a, 
level  of  the  water ; 
b,  swelling  formed  at 
the  upper  denuda- 
tion ;  c,  roots. 


124.  The  three  principal  functions  of  the 
stem  are :  —  (1)  to  serve  as  a  mechanical  sup- 
port and  framework  for  binding  the  other 
organs  together  and  bringing  them  into  the  best  attainable 
relations  with  light  and  air ;  (2)  as  a  water  carrier,  or  pipe 
line,  for  conveying  the  sap  from  the  roots  to  the  parts  where 
it  is  needed ;   and  (3)  as  a  receptacle  for  the  storage  of  foods. 


114 


PRACTICAL   COURSE   IN   BOTANY 


125.  Movement  of  water.  —  It  has  already  been  shown 
(71,  HI)  that  a  constant  interchange  of  Hquid  is  taking  place 
through  the  stem,  between  the  roots,  where  it  is  absorbed  from 
the  ground,  and  the  leaves,  where  it  is  used  partly  in  the  man- 
ufacture of  food.  Just  what  causes  the  rise  of  sap  in  the  stem 
is  one  of  the  problems  of  vegetable  physiology  that  botanists 

have  not  yet  been  able  to 
solve.  There  are,  how- 
ever, certain  forces  at 
work  in  the  plant,  which, 
though  they  may  not  ac- 
count for  all  the  phenom- 
ena of  the  movement, 
undoubtedly  influence 
them  to  a  great  extent. 
From  experiments  58- 
61,  we  can  obtain  an 
idea  of  what  some  of 
these  forces  may  be. 

126.  Direction  of  the 
current.  —  These  experi- 
ments show  that  the  up- 
ward movement  of  crude 
sap  toward  the  leaves  is 
mainly  through  the  ducts 
in  the  woody  portion  of 
the  stem,  while  the  down- 
ward flow  of  elabonated 
sap  from  the  leaves  takes 
place  chiefly  through  the 
soft  bast  and  certain  other  vessels  of  the  cortical  layer.  The 
action  of  the  leaves  in  giving  off  part  of  the  water  absorbed,  as 
shown  in  Exp.  59,  probably  has  also  an  important  influence 
on  the  course  of  sap  movement.  If  loss  of  water  takes  place 
in  any  organ  through  growth  or  other  cause,  the  osmotic  flow 
of  the  thinner  sap  from  the  roots  will  set  in  that  direction. 


Fig.  130. — The  .stump  of  a  larj^e  oak  that 
was  injured  by  lightning  many  years  ago.  The 
interior  is  completely  decayed,  leaving  only 
a  hollow  shell  of  living  tissue,  from  which 
branches  continue  to  put  forth  leaves  year 
after  year. 


THE  STEM 


115 


T27.  Ringing  fruit  trees.  —  The  course  of  the  sap  explains 
why  farmers  sometimes  hasten  the  ripening  of  fruit  by  the 
practice  of  ringing.  As  the  food  material  cannot  pass  below 
the  denuded  ring,  the  parts  above  become  gorged,  and  a  pro- 
cess of  forcing  takes  place.  The  practice,  however,  is  not  to 
be  commended,  except  in  rare  cases,  as  it  generally  leads  to 
the  death  of  the  ringed  stem.  The  portion  below  the  ring 
can  receive  no  nourishment  from  above,  and  will  gradually 
be  so  starved  that  it  cannot  even  act  as  a  carrier  of  crude 
sap  to  the  leaves,  and  so  the  whole  bough  will  perish. 

128.  Sap  movement  not  circulation.  —  It  must  not  be 
supposed  that  this  flow  of  sap  in  plants  is  analogous  to  the 
circulation  of  the  blood  in  animals,  y^  |o  / 
though  frequently  spoken  of  in  pop- 
ular language  as  the  "  circulation  of 
the  sap."  There  is  no  central  organ 
like  the  heart  to  regulate  its  flow,  and 
the  water  taken  up  by  the  roots  does 
not  make  a  continual  circuit  of  the 
plant  body  as  the  blood  does  of  ours, 
but  is  dispersed  by  a  process  of  general 
diffusion,  partly  into  the  air  through 
the  leaves  and  partly  through  the  plant 
body  as  food,  wherever  it  is  needed. 
Figure  131  gives  a  good  general  idea 
of  the  movement  of  sap  in  trees,  the 
arrows  indicating  the  direction  of  the 
movement  of  the  different  substances. 

129.  Unexplained  phenomena.  —  Though  the  forces 
named  above  undoubtedly  exert  a  powerful  influence  over 
sap  movement,  their  combined  action  has  not  been  proved 
capable  of  lifting  the  current  to  a  height  of  more  than  200 
feet,  while  in  the  giant  redwoods  of  California  and  the  tower- 
ing blue  gums  of  Australia,  it  is  known  to  reach  a  height  of 
more  than  400  feet.  The  active  force  exerted  by  the  cell 
protoplasm  has  been  suggested  as  an  efficient  cause,  but  as 


Fig.  131. —  Diagram  show- 
ing general  movement  of  sap. 


116         PRACTICAL  COURSE  IN  BOTANY 

the  upward  flow  takes  place  through  the  cells  of  the  xylem, 
which  contain  no  protoplasm  (116),  this  explanation  is  in- 
adequate, and  we  must  be  content,  in  the  present  state  of  our 
knowledge,  to  accept  the  fact  as  one  which  science  has  yet  to 
account  for. 

Practical  Questions 

1.  Wh.y  will  a  leafy  shoot  heal  more  quickly  than  a  bare  one  ?  (125, 
126;  Exp.  58.) 

2.  Why  does  a  transverse  cut  heal  more  slowly  than  a  vertical  one  ? 
(126,  127.) 

3.  Why  docs  a  ragged  cut  heal  lass  rapidly  than  a  smooth  one  ? 

4.  Why  does  the  formation  of  wood  proceed  more  rapidly  as  the  amount 
of  water  given  off  by  the  leaves  is  increased  ?     (126;  Exp.  59.) 

5.  Why  do  nurserymen  sometimes  split  the  cortex  of  j'oung  trees  in 
summer  to  promote  the  formation  of  wood  ?     (116,  118.) 

6.  What  is  the  advantage  of  scraping  the  stems  of  trees  ? 

7.  Explain  the  frothy  exudation  that  often  appears  at  the  cut  ends  of 
firewood,  and  the  singing  noise  that  accompanies  it.     [120,  124  (2).] 

8.  Of  what  advantage  is  it  to  high  climbing  plants,  like  grape  and 
trumpet  vine  {Tecoma),  to  have  such  large  ducts  ?     (HI,  116,  122.) 

9.  Why  is  the  process  of  layering  more  apt  to  be  successful  if  the  shoot 
is  bent  or  twisted  at  the  point  where  it  is  desired  to  make  it  root  ?  (127; 
Exps.  60,  61.) 

10.  Why  do  oranges  become  dry  and  spongy  if  allowed  to  hang  on  the 
tree  too  long  ?     (72,  126;  Exps.  60,  61.) 

11.  Why  will  corn  and  fodder  be  richer  in  nourishment  if,  at  harvest, 
the  whole  stalk  is  cut  down  and  both  fodder  and  grain  are  allowed  to 
mature  upon  it?     (126,  127;  Exps.  60,  61.) 

12.  Is  the  injury  done  to  plants  by  freezing  due,  as  a  general  thing, 
to  mechanical,  or  to  chemical  action  ?     (33.) 

13.  Why  in  pruning  a  branch  is  it  best  to  make  the  cut  just  above  a 
bud?     (Exps.  60,  61.) 

14.  Why  is  the  rim  of  new  bark,  or  callus,  that  forms  on  the  upper  side 
of  a  horizontal  wound,  thicker  than  that  on  the  lower  side?  (126,  127; 
Exps.  60,  61.) 

15.  Why  is  it  that  the  medicinal  or  other  special  properties  of  plants 
are  found  mostly  in  the  leaves  and  bark,  or  in  the  parts  immediately 
under  the  bark  ?     (120,126.) 

16.  \Vhy  does  testing  the  footstalk  of  a  bunch  of  grapes,  just  before 
ripening,  make  them  sweeter  ?     (127.) 


THE   STEM 


117 


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■  1 

Plate  6.  —  A  white  oak,  one  of  tlic  moiiarchs  of  the  dicotyl  type.  The  owner  of 
the  ground  on  which  this  noble  tree  stands  left  a  clause  in  his  will  bequeathing  it  in 
perpetuity  a  territory  of  8  feet  in  every  direction  from  its  base.  Refer  to  89  and 
decide  whether  such  an  amount  of  standing  room  ia  sufficient  to  secure  the  preser- 
vation of  this  beautiful  object. 


118  PRACTICAL  COURSE   IN   BOTANY 

17.  Is  it  a  mere  superstition  to  drive  nails  into  the  stems  of  plmn  and 
peach  trees  to  make  them  bear  larger  or  more  abundant  fruit  ?    (126,  127.) 

18.  Why  is  a  living  corn  stalk  heavier  than  a  dry  one  ?     (124.) 

19.  Why  is  a  stalk  of  sugar  cane  heavier  than  one  of  corn  ?  Suggestion : 
Which  is  the  heavier,  pure  water,  or  water  holding  solids  in  solution? 

V.    WOOD  STRUCTURE  IN  ITS  RELATION  TO  INDUSTRIAL  USES 

Material.  —  Select  from  the  billets  of  wood  cut  for  the  fire,  sticks  of 
various  kinds  ;  hickory,  ash,  oak,  chestnut,  maple,  walnut,  cherry,  pine, 
cedar,  tulip  tree,  all  make  good  specimens.  Rod  oak  shows  the  medullary 
rays  well.  Get  sticks  of  green  wood,  if  possible,  and  liave  them  planed 
smooth  at  the  ends.  Collect  also,  where  they  can  be  obtained,  waste  bits 
of  dressed  lumber  from  a  carpenter  or  joiner.  If  nothing  better  is  avail- 
able, any  pieces  of  unpainted  woodwork  about  the  schoolroom  will  furnish 
subjects  for  study. 

130.  Detailed  structure  of  a  woody  stem.  ^  Select  a 
good-sized  billet  of  hard  wood,  and  count  the  rings  of  annual 
growth.  How  old  was  the  tree  or  the  bough  from  which  it 
was  taken  ?  Was  its  growth  uniform  from  year  to  year  ? 
How  do  you  know?  Are  the  rings  broader,  as  a  general 
thing,  toward  the  center  or  the  circumference?  How  do 
you  account  for  this  ?  Is  each  separate  ring  of  uniform 
thickness  all  the  way  round?  Mention  some  of  the  cir- 
cumstances that  might  cause  a  tree  to  grow  less  on  one  side 
than  on  the  other.  Are  the  rings  of  the  same  thickness  in 
all  kinds  of  wood  ?  WTiich  are  the  more  rapid  growers,  those 
with  broad  or  with  narrow  rings?  Do  you  notice  any  dif- 
ference in  the  texture  of  the  wood  in  rapid  and  in  slow  grow- 
ing trees?  Which  makes  the  better  timber  as  a  general 
thing,  and  why  ? 

131.  Heartwood  and  sapwood.  —  Notice  that  in  some 
of  your  older  specimens  (cedar,  black  walnut,  barberry, 
black  locust,  chestnut,  oak,  Osage  orange,  show  the  differ- 
ence distinctly)  the  central  part  is  different  in  color  and  text- 
ure from  the  rest.  This  is  because  the  sap  gradually  abandons 
the  center  (116,  123)  to  feed  the  outer  layers,  where  growth 
in  dicotyls  takes  place;   hence,  the  outer  part  of  the  stem 


THE   STEM 


119 


Fig.  132.  —  Cross  section  through  a  black  oak,  showing  heart- 
wood  and  sapwood.    {From  Pinchot,  U.  S.  Dept.  of  Agr.) 


¥iQ.  133.  —  Vertical  aectiou   through  a   black  oak.     {From  Pinchot, 
U.  S.  Dept.  of  Agr.) 


120 


PRACTICAL  COURSE  IN  BOTANY 


usually  consists  of  sapwood,  which  is  soft  and  worthless  as 
timber,  while  the  dead  interior  forms  the  durable  heart- 
wood  so  prized  by  lumbermen.  The  heartwood  is  useful  to 
the  plant  principally  in  giving  strength  and  firmness  to  the 
axis.  It  will  now  be  seen  why  girdling  a  stem,  —  that  is,  chip- 
ping off  a  ring  of  the  softer  parts  all  round,  will  kill  it,  while 
vigorous  and  healthy  trees  are  often  seen  with  the  center  of 
the  trunk  entirely  hollow. 

132.  Different  ways  of  cutting.  —  In  studying  the  vertical 
arrangement  of  stems,  two  sections  are  necessary,  a  radial  and 
a  tangential  one.  The  former  passes  along  the  axis,  splitting 
the  stem  into  halves  (Fig.  135) ;  the  latter  cuts  between  the 

axis  and  the  perimeter,  split- 
ting off  a  segment  from  one 
side  (Fig.  136).  The  appear- 
ance of  the  wood  used  in  car- 
pentry and  joiner's  work  is  due 
largely  to  the  manner  in  which 
the  planks  are  cut. 

133.  The  cross  cut.  —  The 
section  seen  at  the  end  of  a  log 
(Figs.  132,  134)  is  called  by 
carpenters  a  cross  cut.  It 
passes  at  right  angles  to  the 
grain  of  the  wood,  and  severs  what  important  structures? 
(116,  119,  122.)  Examine  a  cross  cut  at  the  end  of  a  rough 
plank,  or"  the  top  of 
a  stump  or  an  old 
fence  post,  and  tell 
why  this  kind  of  cut 
is  seldom  used  in 
carpentry. 

134.  The  tangent 
cut  is  so  called  be- 
cause it  is  made  at     'Z~~',o^ r^  -  .^-r-^^^^.^^-^  .^  ,'  ' " 

Fig.  137.— Tangential  section  of  mountam  ash,  show- 
right    angles    to   the     ing  ends  of  the  meduUary  rays. 


134  135  136 

Figs.  134-136.  —  Diagrams  of  sec- 
tions of  timber:  134,  cross  section ; 
135,  radial :  136,  tangential.  {Fro7n 
PiNCHOT,  U.  S.  Dept.  of  Agr.) 


THE   STEM 


121 


t  rrr 


Fig.  138.  —  Diagram  to  show 
the  common  method  of  sawing  a 
log.  The  circles  represent  rings 
of  annual  growth  :  R,  R,  diam- 
eter of  the  log  ;  r,  r,  r  and  t,  t,  I, 
boards  cut  perpendicular  to  it, 
givdng  for  the  two  or  three  cen- 
tral ones  radial,  for  the  others, 
tangential,  cuts.  The  waste  por- 
tions are  the  "  slabs  "  and  "edg- 
ings," shown  in  the  dark  seg- 
ments at  R,  R,  and  the  small 
triangular  blocks,  e,  c,  e. 


radius  of  a  log.     Repeat  the  geo-  ^  t  rrr 

metrical  principle  upon  which  such 

a  cut  is  described  as  "  tangential." 

It   passes   through    the   medullary 

rays  and  the  annual  rings  diagonally 

(Fig.  136),  and  is  the  cheapest  way 

of  cutting  timber,  "since  the  entire 

log  is  made  into  planks  and  there 

is  no  waste  except  the  "  slabs  "  and 

''  edgings,"  as   shown  in  Fig.  138. 

The  cut  ends  of  the  medullary  rays 

appear  on  the  surface  as  small  lines 

or  slits  (Fig.  137),  and  give  to  this 

kind  of  plank  its  peculiar   grain- 
ing.    The    wavy    or     "  watered " 

appearance    of    the    annual    rings 

(Figs.  133,  136,  140,  141),  so  often 

seen  in  cheap  furniture  and  in  the  woodwork  of  cheaply 

constructed  houses,  is  caused  by  the  tangential  cut,  which 

strikes  them  at  various  angles. 

135.  The  radial,  or  quartered  cut, 
familiar  to  most  of  us  in  the  "  quar- 
tered oak "  of  commerce,  passes 
through  the  center  of  the  log  and 
cuts  the  rings  of  annual  growth  per- 
pendicularly, giving  it  the  "striped" 
appearance  (Fig.  135)  seen  in  the 
best  woodwork.  It  gets  its  name 
from  the  practice  of  dealers  in  first 
sawing  a  log  into  quarters  and  then 
cutting  parallel  to  the  radius  pass- 
ing through  the  middle  of  each 
quarter,  as  shown  in  Fig.  139.  In 
this  way  each  cut  strikes  the  rings 
perpendicularly,  but  except  in  the 
case  of  very  large  logs,  only  narrow 


Fig.  139.  —  Diagram  illustrat- 
ing the  "quartered  "  cut :  d,  d  and 
d'  d',  radial  cuts  (diameters)  by 
which  the  log  is  "  quartered  "  ; 
c,  center  of  the  log  ;  r,  r,  radii 
passing  through  the  middle  of 
each  quarter,  parallel  to  which 
the  planks  f,  t,  t  are  cut.  The 
circles  represent  rings  of  annual 
growth. 


122 


PRACTICAL  COURSE  IN  BOTANY 


planks  can  be  obtained  in  this  manner.  A  better  way  of 
treating  small  logs  is  shown  in  Fig.  138,  where  the  three 
central  planks,  r;r,r,  on  and  near  the  diameter,  will  give  the 
"  quartered  "  effect,  while  the  rest  can  oe  used  for  the  cheaper 
tangential  cuttings.  Examine  a  piece  of  quartered  board,  or 
a  log  of  wood  that  has  been  split  down  the  center,  and  notice 


Fig.  140.  —  Sections  of  sycamore  wood  :    a,  tangential;  h,  radial; 
c,  cross.     {From  Pinchot,  U.  S.  Dept.  of  Agr.) 


Fig.  141.  — Section  of 
U.  S.  Dept.  of  Agr.) 


{From  Pinchot, 


that  the  medullary  rays  appear  as  silvery  bands  or  plates 
(Figs.  140,  141).  This  is  because  the  cut  runs  parallel  to 
them.  It  is  the  medullary  rays  chiefly  that  give  to  commer- 
cial woods  their  characteristic  graining.  Knots,  buds,  and 
other  adventitious  causes  also  influence  it  in  various  degrees. 
136.  The  swelling  and  shrinking  of  timber.  —  The  ca- 
pacity possessed  by  certain  substances  of  bringing  about  an 


THE  STEM 


123 


Fig.  142.  —  Section 
of  tree  trunk  showing 
knot. 


increase  of  volume  by  the  absorption  of  liquids  is  termed 
imbibition.  Care  must  be  taken  not  to  confound  imbibi- 
tion with  capillarity.  (Exp.  53.)  When  liquids  are  carried 
into  a  body  by  capillary  attraction,  they 
merely  fill  up  vacant  spaces  already  exist- 
ing between  small  particles  of  the  substance, 
and  therefore  do  not  cause  any  swelling  or 
increase  in  size.  When  imbibition  takes 
place,  the  molecules^  or  chemical  units  of  the 
liquid,  force  their  way  between  those  of  the 
imbibing  substance,  and  thus,  in  making 
room  for  themselves,  bring  about  an  in- 
crease in  volume  of  the  imbibing  body. 
To  this  cause  is  due  the  alternate  swelling  and  shrinking  of 
timber  in  wet  and  dry  weather. 

137.   Knots.  —  Look  for  a  billet  with  a  knot  in  it.     Notice 
143  144      ^^^  ^^^  rings  of  growth  are  disturbed 

and  displaced  in  its  neighborhood.  If 
the  knot  is  a  large  one,  it  will  itself 
have  rings  of  growth.  Count  them,  and 
tell  what  its  age  was  when  it  ceased  to 
grow.  Notice  where  it  originates. 
Count  the  rings  from  its  point  of  origin 
to  the  center  of  the  stem.  How  old  was 
the  tree  when  the  knot  began  to  form? 
Count  the  rings  from  the  origin  of  the 
knot  to  the  circumference  of  the  stem ; 
how  many  years  has  the  tree  lived  since 
the  knot  was  formed  ?  Does  this  agree 
with  the  age  of  the  knot  as  deduced 
from  its  own  rings?  As  the  tree  may 
continue  to  live  and  grow  indefinitely 
after  the  bough  which  formed  the  knot 
died  or  was  cut  away,  there  will  probably  be  no  corre- 
spondence between  the  two  sets  of  rings,  especially  in  the 
case  of  old  knots  that  have  been  covered  up  and  embedded  in 


Figs.  143-144.  —  Dia- 
grams of  tree  trunks,  show- 
ing knots  of  different  ages  : 
143,  from  tree  grown  in 
the  open;  144,  from  tree 
grown  in  a  dense  forest. 


124  PRACTICAL  COURSE   IN   BOTANY 

the  wood.  The  longer  a  dead  branch  remains  on  a  tree  the 
more  rings  of  growth  will  form  around  it  before  covering  it  up, 
and  the  greater  will  be  the  disturbance  caused  l)y  it.  Hence, 
timber  trees  should  be  i)runed  while  ver^^  3^oung,  and  the 
parts  removed  should  be  cut  as  close  as  possible  to  the  main 
branch  or  trunk.  Sometimes  knots  injure  lumber  very  much 
by  falling  out  and  leaving  the  holes  that  are  often  seen  in  pine 
boards.  In  other  cases,  however,  when  the  knots  are  very 
small,  the  irregular  markings  caused  by  them  add  greatly 
to  the  beauty  of  the  wood.  The  peculiar  marking  of  bird's- 
eye  maple  is  caused  by  abortive  buds  buried  in  the  wood. 

Practical  Questions 

1.  Is  the  swelling  of  wood  a  physical  or  a  physiological  process? 

2.  Does  wood  swell  equally  with  the  grain  and  across  it  ?  (Suggestion : 
test  by  keeping  a  block  under  water  for  10  to  20  days,  measuring  its  dimen- 
sions be^'ore  and  after  immersion.) 

3.  In  building  a  fence,  what  is  the  use  of  "capping"  the  posts?     (133.) 

4.  In  laying  shingles,  why  are  they  made  to  touch,  if  the  work  1:  done 
in  wet  weather,  and  placed  somewhat  apart,  if  in  dry  weather?     (136.) 

5.  What  is  the  difference  between  timber  and  lumber?  Between  a 
plank  and  a  board  ?     Between  a  log,  stick,  block,  and  billet  ? 

6.  Why  does  sap  wood  decay  mjre  quickly  than  heartwood?     (131.) 

7.  Explain  the  difference  between  osmosis,  diffusion,  capillarity,  and 
imbibition.     (9,  56,  57,  136;  E.xp.  53.) 

VI.    FORESTRY 

138.  Practical  bearings.  —  This  part  of  our  subject  is 
closely  related  to  lumbering  and  forestry.  The  business  of 
the  lumberman  is  to  manufacture  growing  trees  into  mer- 
chantable timber,  and  to  do  this  successfully  he  must  under- 
stand enough  about  the  structure  of  wood  to  cut  his  boards 
to  the  best  advantage,  both  for  economy  and  for  bringing  out 
the  grain  so  as  to  produce  the  most  desirable  effects  for 
ornamental  purposes. 

139.  Forestry  has  for  its  object:  (1)  the  preservation 
and  cultivation  of  existing  forests ;    (2)  the  planting  of  new 


THE  STEM 


125 


Plate  7.  — TirnlM-r  iv,-  sp.,il,.,l  l,v  -iAuMn,-  l--  ■mirl,  ;,l,,,„-  i„  ,,,ilv  youth. 
Notice  how  the  cruwdcd  .\  .uin>^;  l  inilicr  in  the  I  .mcLlmmiumI  i-  n-litinti  itcif,  the  lower 
branches  dying  ofY  early  from  ovcrshading,  leaving  tall,  atraight,  clean  bules.  (From 
PiNCHOT,  U.  S.  Dept.  of  Agr.) 


126 


TRACTICAL  COURSE  IN  BOTANY 


ones,  or  the  reforestation  of  tracts  from  which  the  timber  has 
been  destroyed.  Forests  may  be  either  pure,  that  is,  com- 
posed mainly  of  one 
kind  of  tree,  as  a  pine 
or  a  fir  wood  ;  or  mixed, 
being  made  up  of  a  vari- 
ety of  different  growths, 
as  are  most  of  our  com- 
mon hardwood  forests. 
140.  Enemies  of  the 
forest. — -The  first  step 
in  the  preservation  of 
our  forests  is  to  know 
the  dangers  to  be 
j2;uarded  against.  The 
chief  of  these  are* 
<\)  fires;  (2)  the  igno- 
rance or  recklessness  of 
man  in  cutting  for 
commercial  purposes ; 
(3)  fungi;  (4)  injurious  insects;  (5)  sheep,  hogs,  and  other 
animals  that  eat  the  seeds  and  the  young,  tender  growth. 

141.  How  to  protect  the 
forests.  —  The  annual  de- 
struction of  forests  by  fires 
probably  exceeds  that  from 
all  other  causes  combined. 
The  only  effectual  safeguard 
against  this  danger  is  watch- 
fulness on  the  part  of  every- 
hodif.  We  can  each  one  of 
us  help  in  this  work  by  at 
least  being  careful  ourselves 
never  to  kindle  a  fire  in  the 
woods  without  taking  every 
precaution  against  its 


Fig.  145.  —  After  the  forest  fire. 


Oyater  fuugus  ou  Uudeo, 


THE  STEM  127 

spreading.  A  single  match,  or  the  glowing  stump  of  a  cigar, 
carelessly  thrown  among  dry  leaves  or  grass,  may  start  a 
conflagration  that  will  destroy  millions  of  dollars'  worth  of 
standing  timber. 

To  prevent  the  spread  of  fungi,  dead  trees  should  be  re- 
moved, and  broken  or  decayed  branches  trimmed  off  and  the 
cut  surfaces  painted.  Birds  which  destroy  insects  should  be 
protected ;  sheep  and  hogs  should  be  kept  out,  and  dead 
leaves  left  on  the  ground  to  cover  the  roots  and  fertilize  the 
soil  with  the  humus  created  by  their  decay.  Finally,  none 
but  mature  trees  should  be  cut  for  industrial  purposes,  and 
the  cutting  ought  to  be  done  in  such  a  way  that  the  young 
surrounding  growth  will  not  be  injured  by  the  falling 
trunks. 

142.  The  usefulness  of  forests.  —  Aside  from  the  value 
of  their  products,  forests  are  useful  in  many  other  ways. 
They  influence  climate  beneficially  by  acting  as  windbreaks, 
by  giving  off  moisture  (Exp.  58),  by  shading  the  soil,  and 
thus  preventing  too  rapid  evaporation.  Their  roots  also 
help  to  retain  the  water  in  the  soil,  and  by  this  means  tend 
to  prevent  the  washing  of  the  land  by  heavy  rains  and  to 
restrain  the  violence  of  freshets. 

143.  Forests  and  water  supply.  —  It  is  especially  im- 
portant that  the  watershed  of  any  region  should  be  well 
protected  by  forests,  to  prevent  contamination  of  the  streams 
and  to  insure  an  unfailing  supply  of  water  by  checking  the 
escape  of  the  rainfall  from  the  soil. 

Practical  Questions 

1.  Explain  the  difference  between  a  forest,  grove,  copse,  wood,  wood- 
land. 

2.  In  pruning  a  tree  why  ought  the  branch  to  be  cut  as  close  to  the  stock 
as  possible?     (137.) 

3.  Name  the  principal  timber  trees  of  your  neighborhood.  What  gives 
to  each  its  special  value  ? 

4.  Name  six  trees  that  produce  timber  valuable  for  ornament ;  for 
toughness  and  strength. 


128  PRACTICAL  COURSE  IN  BOTANY 

5.  Which  is  the  better  for  timber,  a  tree  grown  in  the  open,  or  one 
grown  in  a  forest,  and  why?     (Plate  7.) 

6.  What  are  the  objects  to  be  attained  in  pruning  timber  trees?  Or- 
chard and  ornamental  trees  ? 

7.  Is  the  outer  bark  of  any  use  to  a  tree,  and  if  so,  what  ? 

8.  Why  should  pruning  not  be  done  in  wet  weather?     [140  (3),  141.] 

9.  Why  should  vertical  shoots  be  cut  off  obliquely?  [133,  140  (3), 
141.] 

Fisld  Work 

(1)  Make  a  study  of  the  various  climbing  plants  of  your  neighborhood 
with  reference  to  their  modes  of  ascent,  and  the  effect,  injurious,  or  other, 
upon  the  plants  to  which  they  attach  themselves.  Note  the  origin  and 
position  of  tendrils,  and  try  to  make  out  what  modification  has  taken 
place  in  each  case.  Consider  the  twining  habit  in  reference  to  parasitism, 
especially  in  the  case  of  soft-stemmed  twiners  when  brought  into  contact 
with  soft-stemmed  annuals.  Observe  the  various  habits  of  stem  growth: 
prostrate,  declined,  ascending,  etc.,  and  decide  what  adaptation  to  cir- 
cumstances may  have  influenced  each  case. 

(2)  Notice  the  shape  of  the  different  stems  met  with,  and  learn  to 
recognize  the  forms  peculiar  to  certain  of  the  great  families.  Observe 
the  various  appliances  for  defense  and  protection  with  which  they  are 
provided,  and  try  to  find  out  the  meaning  of  the  numerous  grooves,  ridges, 
hairs,  prickles,  and  secretions  that  are  found  on  stems.  Alwaj^s  be  on  the 
alert  for  modifications,  and  learn  to  recognize  a  stem  under  any  disguise, 
whether  thorn,  tendril,  foliage,  water  holder,  rootstock,  or  tuber. 

(3)  Note  the  color  and  texture  of  the  bark  of  the  different  trees  you  see 
and  learn  to  distinguish  the  most  important  kinds  : 

(a)  scaly  —  peeling  off  annually  in  large  plates,  as  sycamore,  shagbark- 

hickory ; 
(6)  fibrous  —  detached  in  stiff  threads  and  fibers,  as  grape  ; 

(c)  fissured  —  split  into  large,  irregular  cracks  by  the  growth  of  the 

stem  in  thickness,  as  oak,  chestnut,  and  most  of  our  large  forest 
trees ; 

(d)  membranous  —  separating  in  drj^  films  and  ribbons,  as  common 

})irch  (Betula  alba). 
Observe  the  difference  in  texture  and  appearance  of  the  bark  on  old 
and  young  boughs  of  the  same  species.  Try  to  account  for  the  varying 
thickness  of  the  bark  on  different  trees  and  on  different  parts  of  the  same 
tree.  Notice  the  difference  in  the  timber  of  the  same  species  when  grown 
in  different  soils,  at  different  ages  of  the  tree,  and  in  healthy  and  weakly 
specimens.  Find  examples  of  self-pruning  trees  (Plate  7),  and  explain 
how  the  pruning  was  brought  about. 


THE   STEM  129 

(4)  Select  a  small  plot,  about  a  fourth  of  an  acre,  of  any  wooded  tract 
in  your  neighborhood,  and  make  a  study  of  all  the  trees  and  shrubs  it  con- 
tains. Make  a  list  of  the  different  kinds,  with  the  number  of  each.  Take 
note  of  those  that  .show  themselves,  by  vigor  and  abundance  of  growth, 
best  adapted  to  the  situation.  These  are  the  "climax"  or  dominant 
vegetation  of  the  plot.  Find  out,  if  you  can,  to  what  cause  their  superi- 
ority is  due. 


130 


PRACTICAL  COURSE  IN  BOTANY 


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CHAPTER  V.     BUDS  AND  BRANCHES 

I.    MODES    OF   BRANCHING 

Material.  —  For  determinate  growth,  have  twigs  of  an  alternate  and 
an  opposite-leaved  plant  showing  well-developed  terminal  buds:  hickory, 
sweet  gum,  cottonwood,  poplar,  chestnut,  are  good  examples  of  the 
first ;  maple,  ash,  horse-chestnut,  viburnum,  of  the  second ;  for  the  two- 
forked  kind,  mistletoe,  buckeye,  horse-chestnut,  jimson  weed,  lilac.  For 
showing  indefinite  growth :  rose,  willow,  sumach,  and  ailanthus  are  good 
examples.  Gummy  buds,  like  horse-chestnut  and  poplar,  should  be 
soaked  in  warm  water  before  dissecting,  to  soften  the  gum ;  the 
same  treatment  may  be  applied  when  the  scales  are  too  brittle  to  be 
handled  without  breaking.  Buds  with  heavy  fur  on  the  scales  cannot 
very  well  be  studied  in  section;  the  parts  must  be  taken  out  and 
examined  separately. 


144.   Modes  of  branching.  —  Compare  the  arrangement 
of  the  boughs  on  a  pine,  cedar,  magnolia,  etc.,  with  those 

of  the  elm,  maple,   apple,  or  any  of    our 

common  deciduous  trees.     Draw  a  diagram 

of  each,  showing  the  two  modes  of  growth. 

The  first  represents  the 

excurrent  kind,  from  the 

Latin   excurrere,   to   run 

out ;  the  second,  in  which 

the  trunk  seems   to  di- 
vide  at  a  certain  point 

and    flow    away,    losing 

itself    in    the    branches, 

is      called      deliquescent, 

from  the  Latin  deliques- 

cere,  to  melt  or  flow  away. 
The  great  majority  of   stems,   as  a  little  observation  will 
show,  present  a  combination  of  the  two  modes. 

131 


Fig.  147.  —  Dia- 
gram of  excurrent 
growth. 


Fig.  148.  —  Diagram 
of  deliquescent  growth. 


132 


PRACTICAL  COURSE  IN  BOTANY 


145.  Terminal  and  axillary  buds.  —  Notice  the  large  bud 
at  the  end  of  a  twig  of  hickory,  sweet  gum,  beech,  cotton- 
wood,  etc.  This  is  called  the  terminal  bud  because  it  ter- 
minates its  branch..  Notice  the  scars  left  by  the  leaves  of 
the  season  as  they  fell  away,  and  look  for  small  buds  just 
above  them.  These  are  lateral,  or  axillary,  buds,  so  called 
because  they  spring  from  the  axils  of  the  leaves.  How 
many  leaves  did  your  twig  bear?  Wliat 
difference  in  size  do  you  notice  between 
the  terminal  and  lateral  buds? 

146.   The  leaf  scars.  —  Examine  the  leaf 
scars  with  a  hand  lens,   and  observe  the 
number  and  position  of  the  little  dots  in 
them.      Ailanthus,  varnish   tree,  sumach, 
r       and  China  tree  show  these  very  distinctly. 
r      They  are  called  leaf  traces,  and  mark  the 
points   where    the    fibrovascular    bundles 
from  the  leaf  veins  passed  into  the  stem. 
Fig.  149.  —  Winter    Look  on  the  bark,  or  epidermis,  for  lenticels. 

twig  of  sugar  maple:  ^      -o     j  1  j  tvt    i.-        j.i 

i,  terminal  bud;  ax,        147-   Bud  scalcs  and  scars.  —  Notice  the 
axillary  buds;  Is,  leaf    ^^Q^t  hard  scales  by  which  the  winter  buds 

Bears  ;   tr,  leaf  traces  ;  . 

/,  lenticels ;  rs,  ring  of  are  covered  in  most  of  our  hardy  trees  and 
orprecedin^  seasom '^^  shrubs.  Removo  thesc  from  the  terminal 
one  of  your  specimen,  and  notice  the  ring 
of  scars  left  around  the  base.  Look  lower  down  on  your 
twig  for  a  ring  of  similar  scars  left  from  last  year's  bud. 
Is  there  any  difTerence  in  the  appearance  of  the  bark  above 
and  below  this  ring  ?  If  so,  what  is  it,  and  how  do  you  ac- 
count for  it  ?  Is  there  more  than  one  of  these  rings  of  scars 
on  your  twig,  and  if  so,  how  many  ?  How  old  is  the  twig 
and  how  much  did  it  grow  each  year  ?  Has  its  growth  been 
uniform,  or  did  it  grow  more  in  some  years  than  in  others? 
148.  Arrangement  and  use  of  the  scales.  —  Notice  the 
manner  in  which  the  scales  overlap  so  as  to  "  break  joints," 
like  shingles  on  the  roof  of  a  house,  "Where  the  leaves  are 
opposite,  the  manner  of  superposition  is  very  simple.     Re- 


BUDS  AND  BRANCHES 


133 


[H-H-<^  nip 


Fig.  150.  —  Dia- 
gram of  opposite  bud 
scales. 


move  the  scales  one  by  one,  representing  the  number  and 
position  of  the  pairs  by  a  diagram  after  the  model  given  in 
Fig.  150.  In  the  bud  of  an  alternately  branched  twig  the 
order  will  be  different,  and  the  diagram  must  be  varied  ac- 
cordingly. Do  you  observe  any  difference  _ 
as  to  size  and  texture  between  the  outer 
and  inner  scales  ?  Notice  how  the  former 
inclose  the  tenderer  parts  within  like  a 
protecting  wall.  In  cold  climates  the  outer 
scales  are  frequently 
coated  with  gum,  as  in 
the  horse-chestnut,  for 
greater  security  against 
the  weather.  The  hickory  and  various 
other  trees  have  the  inner  scales  covered 
with  fur  or  down  that  envelops  the  tender 
bud  like  a  warm  blanket. 

149.  Nature  of  the  scales.  —  The  posi- 
tion of  the  scales  shows  that  they  occupy 
the  place  of  leaves  or  of  some  part  of  a 
leaf.  In  expanding  buds  of  the  lilac  and 
many  other  plants,  they  can  be  found  in 
all  stages  of  transition,  from  scales  to 
true  leaves.  In  the  buckeye  and  horse- 
chestnut,  they  will  easily  be  recognized 
as  modified  leaf  stalks  (Fig.  151).  In  the 
tulip  tree,  magnolia,  India  rubber  tree, 
fig,  elm,  and  many  others,  they  represent 
appendages  called  stipules,  often  found  at 
the  bases  of  leaves.  (See  165,  166.)  In 
this  case  a  pair  of  scales  is  attached  with 
each  separate  leaflet,  and  as  the  growing  axis  lengthens  in 
spring,  they  are  carried  apart  by  the  elongation  of  the  inter- 
nodes  so  that  the  scars  are  separated,  a  pair  at  each  node, 
making  rings  all  along  the  stem,  as  shown  in  Fig.  152,  in- 
stead of  having  them  compacted  into  bands  at  the  base  of 


Fig.  151.— Devel- 
opment of  the  parts  of 
the  bud  in  the  buckeye, 
(After  Gray.) 


134 


PRACTICAL  COURSE  IN  BOTANY 


FiG.152.— Stem 
of  tulip  tree :  s,  s, 
scars  left  by  stipular 
scales  ;  /,  I,  leaf  scars. 


the  bud.  These  scars  are  sometimes  very  persistent,  and 
in  the  common  fig  and  magnolia  may  often  be  traced  on 
stems  six  to  eight  years  old.  Do  they  furnish 
any  indication  as  to  the  relative  age  of  the 
different  parts  of  the  stem,  like  the  bands  of 
scars  on  twigs  of  horse-chestnut  and  hickory  ? 
Give  a  reason  for  your  answer.  (Fig.  152.) 
150.  Different  rates  of  growth.  —  Notice 
the  ver}^  great  difference  between  branches 
in  this  respect.  Sometimes  the  main  stem 
will  have  lengthened  from  twenty  to  fifty 
centimeters  or  more  in  a  single  season,  while 
some  of  the  lateral  ones  will  have  grown 
but  an  inch  or  two  in  four  or  five  seasons. 
One  reason  for  this  is  because  the  terminal 
bud,  being  on  the  great  trunk  line  of  sap 
movement,  gets  a  larger  share  of  nourish- 
ment than  the  others,  and  being  stronger 
and  better  developed  to  begin  with.,  starts  out  in  life  with 
better  chances  of  success. 

Make  a  drawing  of  your  specimen,  showing  all  the  points 
brought  out  in  the  examination  just  made.  Cut  sections 
above  and  below  a  set  of  bud  scars  and  count  the  rings  of 
annual  growth  in  each  section.  What  is  the  age  of  each? 
How  does  this  agree  with  your  calculation  from  the  number 
of  scar  clusters  left  by  the  bud  scales  ? 

151.  Irregularities.  —  Take  a  larger  bough  of  the  same 
kind  that  you  hav(?  been  studying,  and  observe  whether  the 
arrangement  of  branches  on  it  corresponds  with  the  arrange- 
ment of  buds  on  the  twig.  Did  all  the  buds  develop  into 
branches?  Do  those  that  did  develop  all  correspond  in  size 
and  vigor?  If  all  the  buds  developed,  how  many  branches 
would  a  tree  produce  every  year? 

In  the  elm,  linden,  beech,  hornbeam,  hazelnut,  willow,  and 
various  other  plants,  the  terminal  bud  always  dies  and  the 
one  next  in  order  takes  its  place,  giving  rise  to  the  more  or 


BUDS  AND  BRANCHES 


135 


Fig.  153.  —  Bud  development 
of  beech :  a,  as  it  is,  many  buds 
failing  to  develop  ;  b,  as  it  would 
be  if  all  the  buds  were  to  live. 


less  zigzag  axis  that  generally  characterizes  trees  of  these 
species.     (Fig.  153.) 

152.  Forked  stems.  —  Take  a  twig  of  buckeye,  horse- 
chestnut,  or  lilac,  ;uul  make  a  care- 
ful sketch  of  it,  showing  all  the 
points  that  were  brought  out  in  the 
examination  of  your  previous  speci- 
men. Which  is  the  larger,  the  lat- 
eral or  the  terminal  bud  ?  Is  their 
arrangement  alternate  or  opposite  ? 
What  was  the  leaf  arrangement? 
Count  the  leaf  traces  in  the  scars ; 
are  they  the  same  in  all  ?  If  all  the 
buds  had  developed  into  branches, 
how  many  would  spring  from  a 
node  ?  Look  for  the  rings  of  scars 
left  by  the  last  season's  bud  scales. 
Do  you  find  any  twig  of  more 
than  one  year's  growth,  as  measured  by  the  scar  rings? 
Look  down  between  the  forks  of  a  branched  stem  for  a 
round  scar.  This  is  not  a  leaf  scar,  as  we  can  see  by  its 
shape,  but  one  left  by  the  last  season's 
flower  cluster.  The  flower,  as  we  know, 
dies  after  perfecting  its  fruit,  and  so  a 
flower  bud  cannot  continue  the  growth  of 
its  axis  as  other  buds  do,  but  has  just  the  op- 
posite effect  and  stops  all  further  growth  in 
that  direction.  Hence,  stems  and  branches 
that  end  in  a  flower  bud  cannot  continue 
to  develop  their  main  axis,  but  their  growth 
is  usually  carried  on,  in  alternate-leaved 
stems,  by  the  nearest  lateral  bud,  or  in 
opposite-leaved  ones,  by  the  nearest  pair 
of  buds.  In  the  first  case  there  results  the  zigzag  spray 
characteristic  of  such  trees  as  the  beech  and  elm  (Fig.  155, 
B) ;  in  the  second,  the  two-forked,  or  dichotomous  branching, 


Fig.  154.  — Two- 
forked  twig  of  horse- 
chestnut. 


136 


PRACTICAL  COURSE  IN  BOTANY 


exemplified  by  the  buckeye,  horse-chestnut,  jimson  weed, 
mistletoe,  and  dogwood  (Fig.  155,  A). 

Draw  a  diagram  of  the  buckeye,  or 
other  dichotomous  stem,  as  it  would  be  if 
all  the  buds  developed  into  branches,  and 
compare  it  with  your  diagrams  of  excurrent 
and  deliquescent  growth.  Draw  diagrams 
to  illustrate  the  branching  of  the  elm, 
beech,  lilac,  linden,  rose,  maple,  or  their 
equivalents. 

153.  Definite  and  indefinite  annual 
growth.  —  The  presence  or  absence  of  ter- 
grams  of  two-forked  minal  buds  givcs  rise  to  another  important 
pointed  bodies  in  the  distinction  in  plant  development  —  that 
forks  shows  where  tor-    ^f  definite  and  indefinite   annual  growth. 

minat  flower  buds  or  *^  i>        ^  • 

flower  clusters  have  Compare  With  any  of  the  twigs  just 
of^eJowth.^''^''''^'"''  examined,  a  branch  of  rose,  honey  locust, 
sumac,  mulberry,  etc.,  and  note  the  differ- 
ence in  their  modes  of  termination.  The  first  kind,  where 
the  bough  completes  its  season's  increase  in  a  definite  time 
and  then  devotes  its  energies  to  developing  a  strong 
terminal  bud  to  begin  the  next  year's  work  with,  are  said 
to  make  a  definite  or  determinate  annual  growth.  Those 
plants,  on  the  other  hand,  which  make  no  provision  for 
the  future,  but  continue  to  grow  till  the  cold  comes 
and  literally  nips  them  in  the  bud,  are  indefinite,  or  in- 
determinate annual  growers.  Notice  the  effect  of  this  habit 
upon  their  mode  of  branching.  The  buds  toward  the  end 
of  each  shoot,  being  the  youngest  and  tenderest,  are  most 
readily  killed  off  by  frost  or  other  accident,  and  hence  new 
branches  spring  mostly  from  the  older  and  stronger  buds 
near  the  base  of  the  stem.  It  is  their  mode  of  branching  that 
gives  to  plants  of  this  class  their  peculiar  bushy  aspect. 
Such  shrubs  generally  make  good  hedges  on  account  of  their 
thick  undergrowth.  The  same  effect  can  be  produced  arti- 
ficially by  pruning. 


BUDS  AND   BRANCHES 


137 


Fig.  156. 


lowing 


the  trend  oi  tl 


154.   Differences  in  the  branching  of  trees.  —  We  are  now 

prepared  to  understand  something  about  the  causes  of  that 

endless   variety   in   the 

spread    of    bough    and 

sweep  of   woody  spray 

that  makes  the  winter 

woods  so  beautiful. 

Where  the  terminal  bud 

is  undisputed  monarch 

of  the  bough,  as  in  the 

pine  and  fir,  or  where  it 

is  so  strong  and  vigor- 
ous as  to  overpower  its 

weaker     brethren    and 

keep  the  lead,  as  in  the 

magnolia,  tulip  tree,  and  holly,  we  have  excurrent  growth. 

In  plants  like  the  oak  and  apple,  where  all  the  buds  have 
a  more  nearly  equal  chance,  the  lateral 
branches  show  more  vigor,  and  the  result 
is  either  deliquescent  growth,  or  a  mixture 
of  the  two  kinds.  In  the  elm  and  beech, 
where  the  usurping  pseudo-terminal  bud 
keeps  the  mastery,  but  does  not  completely 
overpower  its  fellows,  we  find  the  long, 
sweeping,  delicate  spray  characteristic  of 
those  species.  Examine  a  sprig  of  elm, 
and  notice  further  that  the  flower  buds  are 
all  down  near  the  bas6  of  the  stem,  while 
the  leaf  buds  are  near  the  tip.  The  chief 
development  of  the  season's  growth  is  thus 
thrown  toward  the  end  of  the  branch,  giv- 
ing rise  to  that  fine,  feathery  spray  which 
makes  the  elm  an  even  more  l^eautiful 
object  in  winter  than  in  summer  (Fig.  158). 
An  examination  of  the  twigs  of  other  trees  will  bring  out  the 

various  peculiarities  that  affect  their  mode  of  branching.    The 


FiQ.  157.  — Winter 
spray  of  ash,  an  op- 
posite-leaved tree. 


138  PRACTICAL  COURSE   IN  BOTANY 

angle,  for  instance,  which  a  twig  makes  with  its  bough  has  a 
great  effect  in  shaping  the  contour  of  the  tree.  Compare  in 
this  respect  the  elm  and  hackberry; 
the  tulip  tree  and  willow ;  ash  and  hick- 
ory. As  a  general  thing,  acute  angles 
produce  slender,  flowing  effects;  right 
or  obtuse  angles,  more  bold  and  rugged 
outlines. 

Practical  Questions 

1.  Has  the  arrangement  of  leaves  on  a  twig 
anything  to  do  with  the  way  a  tree  is  branched? 
(145,  151,  152.) 

2.  Why  do  most  large  trees  tend  to  assume 
Fig.  158.  —Winter  spray     tlie  excurrent,  or  axial,  mode  of  growth  if  let 

alone?     (150,154.) 

3.  If  you  wished  to  alter  the  mode  of  growth,  or  to  produce  what  nur- 
serymen call  a  low-headed  tree,  how  would  you  prune  it?     (152,  153.) 

4.  Would  you  top  a  timber  tree?     (152,  153.) 

5.  Are  low-headed  or  tall  trees  best  for  an  orchard  ?     Why  ? 

6.  Why  is  the  growth  of  annuals  generally  indefinite  ? 

7.  Name  soi-ie  trees  of  your  neighborhood  that  are  conspicuous  for 
their  graceful  winter  spraJ^ 

8.  Name  some  that  are  characterized  by  sharpness  and  boldness  of  outline 

9.  Account  for  the  peculiarities  in  each  case. 

n.    BUDS 

Material.  —  Expanding  leaf  and  flower  buds  in  different  stages  of 
development ;  large  ones  show  the  parts  best  and  should  be  used  where 
attainable.  Some  good  examples  for  the  opposite  arrangement  are 
horse-chestnut,  maple,  lilac,  ash;  for  the  alternate:  hickory,  sweet  gum, 
balsam  poplar,  beech,  elm.  Where  material  is  scarce,  the  twigs  used  in  the 
last  section  may  be  placed  in  water  and  kept  till  the  buds  begin  to  expand. 

155.  Folding  of  the  leaves.  —  Remove  the  scales  from  a 
bud  of  horse-chestnut  nearly  ready  to  open,  and  notice  the 
manner  in  which  the  young  leaves  are  folded.  This  is  called 
vernation,  or  prefoliation,  words  meaning  respectively  "  spring 
condition "  and  "  condition  preceding  the  leaf."  Leaves 
are  packed  in  the  bud  so  as  to  occupy  the  least  space  possible, 
and  in  different  plants  they  will  be  found  folded  in  a  great 


BUDS   AND   BRANCHES 


139 


Fig.  159.  —  Expand- 
ing bud  of  English  wal- 
nut, showing  twice  con- 
duplicate  vernation. 


Fig.  160.  — a 
partly  expanded 
leaf  of  beech, 
showing  plicate- 
conduplicate 
vernation. 


many  different  ways,  according  to  the  shape 
and  texture  of  the  leaf  and 
the  space  available  for  it  in 
the  bud.  When  doubled  back 
and  forth  like  a  fan,  or  crum- 
pled and  folded  as  in  the 
buckeye,  horse-chestnut,  and 
maple,  the  vernation  is  plicate 
(Figs.  160,  162). 

156.   Position  of  the  flower 
cluster.  —  What  do  you  find 
within  the  circle  of  leaves? 
Examine  one  of  the  smaller 
axillary  buds,  and  see  if  you  find  the  same  object  within  it. 
If  you  are  in  any  doubt  as  to  what  this  object  is,  examine 
a  bud  that  is  more  expanded,  and  you  will  have  no  difficulty 
in  recognizing  it  as  a  rudimentary  flower 
cluster.     Notice  its  position  with  refer- 
ence to  the  scales  and  leaves.     If  at  the 
center  of  the  bud,  it  will,  of  course,  termi- 
nate its  axis  when  the 
bud  expands,  and  the 
growth  of  the  branch 
will   culminate   in  the 
flower.    The  branching 
of   any   kind   of  stem 
that    bears    a    central 
flower  cluster  must, 
then,  be  of  what  order  ? 
Compare   your    draw- 
ings with  the  section  of 
a    hyacinth    bulb,  or 
jonquil,  and  note  the 
similarity   in    position 
of  the  flower  clusters. 
In  a  bud  of  the  hick- 


162 


Figs.  161, 162.  — Buds 
of  maple  :  161,  vertical 
BBction  of  a  twig ;  162, 
cross  section  through 
bud,  showing  folded 
leaves  in  center  and  scales 
surrounding  them. 


Fig.  163. -Ver- 
tical section  of  hick- 
ory bud:  a,  furry  in- 
ner scales ;  /;,  outer 
scales  ;  I,  folded  leaf ; 
r,  receptacle. 


140  PRACTICAL  COURSE   IN   BOTANY 

ory,  walnut,  oak,  etc.,  the  position  of  the 
flower  clusters  is  different  from  that  of 
flowers  in  the  buds  of  lilac  and  horse-chest- 
nut. Look  for  a  bud  containing  them,  and 
find  out  where  they  occur.  Can  the  axis  con- 
tinue to  grow  after  flowering,  in  this  kind  of 
stem?  Give  a  reason  for  your  answer.  Make 
sketches  in  transverse  and  longitudinal  sec- 
tion (see  Figs.  102,  163)  of  two  different 
kinds  of  buds,  illustrating  the  terminal  and 
axillary  position  of  the  flower  cluster. 

157.   Dormant  buds.  —  A  bud  may  often 

lie  dormant  for  months  or  even  years,  and 

then,  through  the  injury  or  destruction  of  its 

stronger  rivals,  or  some  other  favoring  cause, 

develop  into  a  branch.     Such  buds  are  said 

to  be  latent  or  dormant.     The  sprouts  that 

often  put  up  from  the  stumps  of  felled  trees 

Fig.  1G4.  — Twig  originate  from  this  sourcc. 

tj'l^it^;       158.   Supemumerarybuds.-Wheremore 

bud.  b;  rs,  ring  of  than  ouc  bud  dcvclops  at  a  node,  as  is  so 

scars    left     by     last        n,  ,-,  •        ,^  ^  ^         ^ 

year's  bud  scales,  otteu  the  casc  m  the  oak,  maple,  honey 
(After  Gray.)  locust,  etc,  all  exccpt  the  uomial  one  in  the 

axil  are  supernumerary  or  accessory.  These  must  not  ])e  con- 
founded with  adventitious  buds  —  those  that  occur  elsewhere 
than  at  a  node. 

Practical  Questions 

1.  Would  protected  buds  be  of  any  use  to  annuals  ?    Why,  or  why  not  ? 

2.  Of  what  use  is  the  gummy  coating  found  on  the  buds  of  the  horse- 
chestnut  and  bahn  of  Gilcad  ?     (148.) 

3.  Can  you  name  any  plants  the  buds  of  which  serve  as  food  for  man  ? 

4.  How  do  flower  buds  differ  in  shai)e  from  leaf  buds  ? 

5.  At  what  season  can  the  leaf  bud  and  the  flower  bud  first  be  dis- 
tinguished ?     Is  it  the  same  for  all  flowering  plants  ? 

6.  Watch  the  different  trees  al^out  your  home,  and  see  when  the  bud3 
that  are  to  develop  into  leaves  and  flowers  the  next  season  arc  formed  in 
each  species. 


BUDS  AND   BRANCHES 


141 


III.    THE   BRANCHING    OF   FLOWER   STEMS 


Material.  —  Typical  flower  clusters  illustrating  the  definite  and 
indefinite  modes  of  inflorescence.  Some  of  those  mentioned  in  the  text 
are:  — 

Indefinite:  hyacmth,  shepherd's  purse,  wallflower,  carrot,  lilac,  blue 
grass,  smartwecd  (Polygonum),  wheat,  oak,  willow,  clover. 

Definite:  chickweed,  spurge  {Euphorbia),  comfrey,  dead  nettle,  etc. 
Any  examples  illustrating  the  principal  kinds  of  cluster  will  answer. 

159.  Inflorescence  is  a  term 
used  to  denote  the  position  and 
arrangement  of  flowers  on  the 
stem.  It  is  merely  a  mode  of 
branching,  and  follows  the  same 
laws  that  govern  the  branching 
of  ordinary  stems. 

The  stalk  that  bears  a  flower 
is  called  the  peduncle.  In  a 
cluster  the  main  axis  is  the  com- 
mon peduncle,  and  the  separate 
flower  stalks  are  pedicels.  A  sim- 
ple leafless  flower  stalk  that  rises 
directly  from  the  ground,  like 
those  of  the  dandelion  and  daffo- 
dil, is  called  a  scape  (Fig.  165). 

160.  Two  kinds  of  inflores- 
cence. —  The  growth  of  flower  stems,  like  that  of  leaf  stems, 

is  of  two  principal  kinds,  definite  and 
indefinite,  or,  as  it  is  frequently  ex- 
pressed, determinate  and  indetermi- 
nate. The  simplest  kind  of  each  is 
the  solitary,  a  single  flower  either 
terminating  the  main  axis,  as  the 
tulip,  daffodil,  trillium,  magnolia, 
etc.,  or  springing  singly  from  the  axils,  as  the  running  peri- 
winkle, moneywort,  and  cotton. 


Fig.    165.  - 
flower  of  a  lily. 


Solitary      terminal 


Fig.  160.  —  Indeterminate 
inflorescence  of  moneywort. 
(After  Gray.) 


142 


PRACTICAL  COURSE   IN  BOTANY 


i6i.  Indeterminate  inflorescence  is  always  axillary, 
since  the  production  of  a  terminal  flower  would  stop  further 
growth  in  that  direction  and  thus  terminate  the  development 
of  the  axis.  The  raceme  is  the  typical 
flower  cluster  of  the  indefinite  sort.  In 
such  an  arrangement  the  oldest  flowers 
are  at  the  lower  nodes,  new  ones  appear- 
ing only  as  the  axis  lengthens  and  pro- 
duces new  internodes.  The  little  scale  or 
hract  usually  found  at  the  base  of  the  pedi- 
cel in  flower  clusters  of  this  sort  is  a  re- 
duced leaf,  and  the  fact  that  the  flower 
stalk  springs  from  the  axil  shows  it  to  be 
of  the  essential  nature  of  a  branch. 
When  the  flowers  are  sessile  and  crowded 
on  the  axis  in  various  degrees,  the  cluster 
produced  may  be  a  spike,  as  seen  in  the 
plantain,  knotweed,  etc.,  or  a  head,  like 
that  of  the  clover,  buttonwood,  and  syca- 
more. The  catkins  that  form  the  characteristic  inflorescence 
of  most  of  our  forest  trees  are  merely  pendant  spikes.  The 
corymb  is  a  modification 
of  the  raceme  in  which 
the  lower  pedicels  are 
elongated  so  as  to  place 
their  flowers  on  a  level 
with  those  of  the  upper 
nodes,  making  a  convex, 
or  more  or  less  flat- 
topped  cluster,  as  in  the 
wall-flowor  and  haw- 
thorn. The  umbel  dif- 
fers from  the  corymb  in 
having  the  pedicels  with 
their  bracts  all  gathered 

at    the     top     of     the    pe-  Fig,  leS.  —  Catkins  of  aspen. 


Fi(i.  167.  —  Raceme 
of  milk  vetch  (Astraga- 
lus). 


BUDS  AND  BRANCHES 


143 


Fig.  169.  — Corymb 
of  plum  blossoms. 


Umbel  of  milk- 


duncle,  from  which  they  spread  in  every  direction  Uke  the 
rays  of  an  umbrella,  as  the  name  imphes.  This  is  the  preva- 
lent type  of  flower  cluster  in  the  parsley  family,  which  takes 
its  botanical  name,  Umbelliferce,  from 
its  characteristic 
form  of  inflores- 
cence. The  pedi- 
cels of  an  umbel 
are  called  rays,  and 
the  circle  of  bracts 
at  the  base  of  the 
cluster  is  an  invo- 
lucre. 

162.  Determi- 
nate, or  cymes  e, 
inflorescence.  —  In  the  cyme,  the  typical  cluster  of  the  de- 
terminate kind,  the  older  blossoms  in  the  center,  being  ter- 
minal, stop  the  axis  of  growth  in  that  direction  and  force  the 
stem,  in  continuing  its  growth,  to  send  out  side  branches 
from  the  axils  of  the  topmost  leaves,  in 
a  manner  precisely 
similar  to  the  two- 
forked  branching  of 
stems  like  the  horse- 
chestnut  and  jimson 
weed.  "WTien  the  older 
peduncles  are  length- 
ened as  described  in 
161 ,  a  flat-topped  cyme 
is  produced,  which  is 
—  Panicin  <^i^^i"Siii>^hed  from  the 
of  grass,  a  rompouiid  coryiiil)  by  its  ordcr  of 

cluster  of  the  racemose    n 

flowering 


type. 

center, 
order. 


while 


the  oldest 
blossoms  being  at  the 
the   corymb    they  appear 


Fig.  172.—  Flat-topped 
cynu-  of  sncozcwecd. 


the 


A  peculiar  form  of  cyme  is  found  in  the  scorpioid 


144 


PRACTICAL  COURSE   IN   BOTANY 


Fig.  173." — Scorpioid  cyme. 

or  coiled  inflorescence  of  the  pink-root  {Spigelia),  heliotrope, 
comfrey,  etc.  Its  structure  will  be  made  clear  by  an  inspec- 
tion of  Figs.  174-176. 


Figs.  174-176.  —  Diagrams  of  cymosc  inflorescence,  with  flowers  numbered  in  the 
order  of  their  development :  174,  cyme  half  developed  (scorpioid) ;  175,  a  flat-topped 
or  corymbose  cyme  ;  176,  development  of  a  typical  cyme. 

163.  The  nature  of  flower  stems.  —  A  comparison  of 
the  types  of  inflorescence  with  the  modes  of  branching  in 
ordinary  stems  (144,  152,  153)  will  show  a  strict  corre- 
spondence between  them.  Both  bear  leaves  and  buds,  and 
the  individual  flowers  of  a  cluster  usually  spring  from  the 


BUDS  AND  BRANCHES  145 

axils  of  leaves  or  from  bracts,  which  are  merely  reduced 
leaves.  What,  then,  is  the  essential  nature  of  flower  stems  ? 
164.  Significance  of  the  clustered  arrangement.  —  As  a 
general  thing  the  clustered  arrangement  marks  a  higher  stage 
of  development  than  the  solitarj^,  just  as  in  human  life  the 
rudest  social  state  is  a  distinct  advance  upon  the  isolated 
condition  of  the  savage.  In  plant  life  it  is  the  beginning  of 
a  system  of  cooperation  and  division  of  labor  among  the  as- 
sociated members  of  the  flower  cluster,  as  will  be  seen  later 
when  we  take  up  the  study  of  the  flower. 

Practical  Questions 

1.  Name  as  many  solitary  flowers  as  you  can  think  of. 

2.  Do  you,  as  a  rule,  find  very  small  flowers  solitary,  or  in  clusters  ? 

3.  Would  the  separate  flowers  of  the  clover,  parsley,  or  grape  be  readily 
distinguished  by  the  eye  among  a  mass  of  foliage  ? 

4.  Should  you  judge  from  these  facts  that  it  is,  in  general,  advantageous 
to  plants  for  their  flowers  to  be  conspicuous  ? 

Field  Work 

(1)  In  connection  with  144-154,  the  characteristic  modes  of  branch- 
ing among  the  common  trees  and  shrubs  of  each  neighborhood  should  be 
observed  and  accounted  for.  The  naked  branches  of  the  winter  woods 
afford  exceptional  opportunities  for  studies  of  this  kind,  which  cannot 
well  be  carried  on  except  out  of  doors.  Note  the  effect  of  the  mode  of 
branching  upon  the  general  outline  of  the  tree ;  compare  the  direction  and 
mode  of  growth  of  the  larger  boughs  with  that  of  small  twigs  in  the  same 
species,  and  see  if  there  is  any  general  correspondence  between  them ;  note 
the  absence  of  fine  spray  on  the  l:)oughs  of  large-leaved  trees,  and  account 
for  it.  Account  for  the  flat  sprays  of  trees  like  the  elm,  beech,  hackberry, 
etc. ;  the  irregular  stumpy  branches  of  the  oak  and  walnut ;  the  stiff 
straight  twigs  of  the  ash ;  the  zigzag  switches  of  the  black  locust,  Osage 
orange,  elm,  and  linden.  Measure  the  twigs  on  various  species,  and  see 
if  there  is  any  relation  between  the  length  and  thickness  of  branches. 
Notice  the  different  trend  of  the  upper,  middle,  and  lower  boughs  in  most 
trees,  and  account  for  it.  Observe  the  mode  of  branching  of  as  many 
different  species  as  possible  of  some  of  the  great  botanical  groups  of  trees ; 
the  oaks,  hickories,  hawthorns,  and  pines,  for  instance,  and  notice  whether 
it  is,  as  a  general  thing,  uniform  among  the  species  of  the  same  group,  and 
how  it  differs  from  that  of  other  groups. 


146  PRACTICAL   COURSE    IN   BOTANY 

(2)  In  connection  with  155-158,  buds  of  as  many  different  kinds  as 
possible  should  be  examined  with  reference  to  their  means  of  protection, 
their  vernation  and  leaf  arrangement,  and  the  resulting  modes  of  growth. 
Compare  the  folding  of  the  cotyledons  in  the  seed  with  the  veination  of 
the  same  plants,  and  observe  whether  the  folding  is  the  same  throughout 
a  whole  group  of  related  plants,  or  only  for  the  same  species.  Notice  which 
modes  seem  to  b(^  most  prevalent.  Select  a  twig  on  some  tree  near  your 
home  or  your  schoolhouse,  and  keep  a  record  of  its  daily  growth  from  the 
first  sign  of  the  unfolding  of  its  principal  bud  to  the  full  development  of 
its  leaves.  Any  study  of  buds  should  include  an  observation  of  them  in 
all  stages  of  development. 

(3)  With  160-165,  study  the  inflorescence  of  the  common  plants  and 
weeds  that  happen  to  be  in  season,  until  you  have  no  difficulty  in  distin- 
guishing between  the  definite  and  indefinite  sorts,  and  can  refer  any 
ordinary  cluster  to  its  proper  form.  Notice  whether  there  is  any  tendency 
to  uniformity  in  the  mode  of  inflorescence  among  flowers  of  the  same  fam- 
ily. Consider  how  each  kind  is  adapted  to  the  shape  and  habit  of  the 
flowers  composing  it,  and  what  particular  advantage  each  of  the  specimens 
examined  derives  from  the  way  its  flowers  are  clustered.  In  cases  of  mixed 
inflorescence,  see  if  you  can  discover  any  reason  for  the  change  from  one 
form  to  the  other. 


CHAPTER  VI.    THE  LEAF 


I.   THE   TYPICAL   LEAF  AND   ITS   PARTS 


Material.  —  Leaves  of  different  kinds  showing  the  various  modes  of 
attachment,  shapes,  texture,  etc.  For  stipules,  leaves  on  very  young 
twigs  should  be  selected,  as  these  bodies  often  fall  away  soon  after  the 
leaves  expand.  The  rose,  Japan  quince,  willow,  strawberry,  pea,  pansy, 
and  young  leaves  of  beech,  apple,  elm,  tulip  tree,  India  rubber  tree, 
magnolia,  knotweed,  furnish  good  examples  of  stipules.  For  the  different 
orders  of  leaf  arrangement,  lilac,  maple,  spurge,  trillium,  cleavers  (Galium) 
show  the  opposite  and  whorled  kinds.  Elm,  basswood,  grasses ;  alder, 
birch,  sedges ;  peach,  apple,  cherry,  show  respectively  for  each  group  the 
three  principal  orders  of  alternate  arrangement. 

165.  Parts  of  the  leaf.  —  Examine  a  young,  healthy  leaf 
of  apple,  quince,  or  elm,  as  it  stands  upon  the  stem,  and 
notice  that  it  consists  of  three  parts :  a 
broad  expansion  called  the  blade;  a  leaf 
stalk  or  petiole  that  attaches  it  to  the 
stem ;  and  two  little  leaflike  or  bristle-like 
bodies  at  the  base,  known 
as  stipules.  Make  a 
sketch  of  any  leaf  pro- 
vided with  all  these  parts, 
and  label  them,  respec- 
tively, blade,  petiole,  and 
stipules.  These  three  parts  make  up  a  per- 
fect or  typical  leaf,  but  as  a  matter  of  fact, 
one  or  more  of  them  is  usually  wanting. 

166.  Stipules.  —  The  office  of  stipules, 
when  present,  is  generally  to  subserve  in 
some  way  the  purposes  of  protection.  In  many  cases,  as  in 
the  fig,  elm,  beech,  oak,  magnoHa,  etc.,  they  appear  only  as 
protective  scales  that  cover  the  bud  during  winter,  and  fall 

147 


Fig.  177.— a  typi- 
cal leaf  and  its  parts: 
b,  blade ;  p,  petiole ; 
s,  s,  stipules. 


Fui.  178.  — Spiuy 
stipules  of  clotbur. 


148 


PRACTICAL   COURSE   IN   BOTANY 


away  as  soon  as  the  leaf  expands.  When  persistent,  that  is, 
enduring,  they  take  various  forms  according  to  the  purposes 
they  serve.  But  under  whatever  guise  they  occur,  their 
true  nature  may  be  recognized  by  their  position  on  each  side 
of  the  base  of  the  petiole,  and  not  in  the  axil,  or  angle  formed 
by  the  leaf  with  the  stem.     (149.) 

167.  Leaf  attachment.  —  The  normal  use  of  the  petiole  is 
to  secure  a  better  light  exposure  for  the  leaves,  but,  like  other 
parts,  it  is  subject  to  modifications,  and  is  often  wanting 


Fig.    179.—  Adnate 
stipules  of  clover. 


Fig.  180.  —  Leaves  of 
smilax,  showing  stipular 
tendrils. 


Fig.  181.  — Leafy 
stipules  of  Japan 
quince. 


altogether.  In  this  case  the  leaf  is  said  to  be  sessile,  that  is, 
seated,  on  the  stem,  and  the  leaf  bases  are  designated  by 
various  terms  descriptive  of  their  mode  of  attachment.  The 
meaning  of  these  terms,  when  not  self-explanatory,  can  best 
be  learned  by  a  comparison  of  living  specimens  with  Figs. 
184-187. 

168.  Arrangement  of  leaves  on  the  stem.  —  The  mode 
of  attachment  is  something  quite  distinct  from  the  mode  of 
leaf  arrangement  on  the  stem,  or  phyllotaxy,  as  it  is  termed 
by  botanists.  It  was  seen  in  148  that  this  takes  place  in  two 
different  ways,  the  alternate  and  opposite.  These  two  kinds 
of  arrangement  represent  the  principal  forms  of  leaf  disposi- 


THE   LEAF 


149 


tion  on  the  stem,  the  different  varieties  of  each  depending  on 
the  manner  in  which  the  leaves  are  distributed. 

Where  three  or  more  occur  at  a  node,  as  in  the  trilUum 
and  cleavers  {Galium),  they  constitute  a  whorl,  which  is  only 


Figs.  182-187.  —  Petioles,  and  leaf  attachmeut :  182,  petioles  of  jasmine  night- 
shade (Solanum  jasminoides)  acting  as  tendrils;  183,  acacia,  showing  petiole 
transforraed  to  leaf  blade;  184,  sessile  leaves  of  epilobium  ;  185,  clasping  leaf  of 
laetuca;  186,  perfoliate  leaves  of  luoilaria;  187,  peltate  leaf  of  tropueolum.  (182  and 
186  after  Gray.) 

a  variant  of  the  opposite  arrangement.  There  is  no  limit  to 
the  number  of  leaves  that  may  be  in  a  whorl  except  the  space 
around  the  stem  to  accommodate  them. 

The  phyllotaxy  of  alternate  leaves  is  more  complicated. 


150 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  188.  — Whorlcd 
leaves  of  Indian  cucum- 
ber. 


The  different  forms  are  characterized  by 
the  angular  distance  between  the  points 
of  leaf  insertion  around  the  stem.  In  the 
olni,  ))asswood,  and  most  grasses,  they  are 
distributed  in  two  rows  or  ranks  on  op- 
posite sides  of  the  stem,  each  just  half 
way  round  the  circumference  from  the 
one  next  in  succession  (Fig.  189),  the 
third  in  vertical  order  standing  directly 
over  the  first.  In  most  of  our  common 
trees  and  shrubs  five  leaves  are  passed 
in  making  two  turns  round  the  stem, 
the  sixth  leaf  in  vertical  order  stand- 
ing over  the  first.  This  is  called  the  five-ranked  arrange- 
ment, and  is  the  most 
common  order  among 
dicotyls. 

169.  Relation  be- 
tween the  shape  and 
arrangement  of  leaves. 
■ —  Phyllotaxy  is  of  im- 
portance chiefly  on  ac- 
count of  its  influence 
on  the  light  relation  of 
leaves.  A  compact, 
close-ranked  arrange- 
ment tends  to  shut  off 
the  light  from  the  lower 
nodes,  and  hence,  in 
plants  where  it  pre- 
vails, the  leaves  are  apt 
to  be  long  and  narrow 
in    proportion   to    the 

frequency    of    the    Ver-         Fig.  189.  — Twigof  ahackben-y  (Ce«iscmerea), 

tical  rows.     The  VUCCa  showing  the  two-ranked  arrangement.    Notice  how 

in  t^*^  position  of  the  stems  and  branches  of  the  main 

oleander,   C  anada  nea-  axis  corresponds  to  that  of  the  leaves. 


THE  LEAF 


161 


Plate.  9.- — Vegetation  of  a  moist,  shady  ravine.  Notice  the  expanded  surface  of 
the  leaf  blades  and  the  long  internodes  that  separate  the  individual  leaves.  (From 
Rep't.  Mo.  Botanical  Garden.) 


152 


PRACTICAL  COURSE  IN  BOTANY 


^ 


K 


bane  and  bitterweed  {Helenium 
ienuijolium) ,  illustrate  this  relation. 

On  the  other  hand,  when  the  leaves 
are  large  and  rounded  in  outline,  as 
those  of  the  sunflower,  hollyhock,  and 
catalpa,  they  are  usually  separated 
by  longer  internodes,  or  their  blades 
are  cut  and  incised  so  that  the  sun- 
light easily  strikes  through  to  the 
low^er  ones. 

170.  Other  external  characteristics 
to  be  observed  in  leaves  are :  — 

(1)  General  Outline :   whether  round,  oval,  heart-shaped, 
etc.  (Figs.  191-197). 

(2)  Margins:    whether    unbroken    {entire),    or   variously 
toothed  and  indented.     (Figs.  198-202.) 


Fig.  190.  —  Narrow  leaves 
in  crowded  vertical  rows. 


Figs.  191-197.  —  Shapes  of  leaves  :  191,  lanceolate ;    192,  spatulate;    193,  o-val; 
194,obovate;  195,  kidney-shaped ;  196,  deltoid;  197,lyrate.     (191-195  a/<erGiwY.) 

(3)  Texture:    whether    thick,    thin,    soft,   hard,    fleshy, 
leathery,  brittle. 

(4)  Surface:    smooth,  shining,  dull,  wrinkled,  hairy,  or 
otherwise  roughened. 


THE   LEAP 


153 


198    199    200  201      202 
Figs.  198-202.— Margins  of 
leaves :    198,  serrate ;    199,  den- 
tate ;  200,  crenate ;  20 1 ,  undulate ; 
202,  sinuate.    (After  Gray.) 


Not  only  do  leaves  of  different 

kinds  exhibit  these  characteristics 

in  varying  degrees,  but  young  and 

old  leaves,  or  those  on  young  and 

old  plants  of  the  same  kind,  often 

differ  from  each  other  in  color,  size, 

shape,  texture,  mode  of  attachment, 

and  the  like,  to  such  a  degree  (Figs. 

203,   204)    that    one  not  familiar 

with   them   in  both  stages  would 

hardly  recognize  them  as   belonging  to  the  same  species. 

The  young  leaves 
of  eucalyptus,  mul- 
berry, and  some  oaks 
afford  conspicuous 
examples  of  such 
differences,  and  they 
exist  between  the 
cotyledons  and  ma- 
ture leaves  of  most 
plants. 

Can  you  see  any 
benefit,  in  the  case 
of  the  plant  whose 
leaves  you  are.  study- 
ing, that  could  be 
derived  from  such  of 
the  characteristics 
above  as 
they  may  exhibit? 


203 


204 


Figs.  203,  204.  —  Leaves  of  paper  mulberry  tree:  i-ioTvipfl 
203,  leaf  from  an  old  tree ;  204,  leaf  from  a  two-year- 
old  sprout. 


Practical  Questions 

I.  Tell  the  nature  and  use  of  the  stipules  in  such  of  the  following  plants 
as  you  can  find  :  tulip  tree  ;  fig ;  beech  ;  apple  ;  willow  ;  pansy ;  garden 
pea ;  Japan  quince  {Pijrus  Japonica) ;  sycamore ;  rose ;  paper  mulberry 
(Broicssonetia) . 


154  PRACTICAL  COURSE  IN  BOTANY 

2.  How  would  you  distinguish  between  a  chinquapin,  a  chestnut,  a 
chestnut  oak,  and  a  horse-chestnut  tree  by  their  leaves  alone  ?  By  their 
bark  and  branches  ?  Between  a  hickory,  ash,  common  elder,  box  elder, 
ailanthus,  sumach?     Between  beech,  birch,  elm,  hackberry,  alder? 

(Any  other  sets  of  leaves  may  be  substituted  for  those  named,  the  object 
being  merely  to  form  the  habit  of  distinguishing  readily  the  differences 
and  resemblances  among  those  that  bear  some  general  likeness  to  one 
another.) 

3.  From  the  study  of  these  or  similar  specimens,  would  you  conclude 
that  resemblances  in  leaves  are  confined  to  those  of  closely  related  kir.ds  ? 

4.  Name  some  causes  independent  of  botanical  relationship  that  might 
influence  them.     (169,  170;  Exps.  48,  57.) 

5.  Do  you  find,  as  a  general  thing,  more  leaves  with  stipules  or  without  ? 

6.  Is  their  absence  from  a  mature  leaf  always  a  sign  that  it  is  really 
exstipulate?     (166.) 

7.  Can  you  trace  any  line  of  development  through  intervening  forms 
from  a  merely  sessile  leaf,  like  that  of  the  pimpernel  or  specularia,  to  a 
peltate  one?     (Figs.  184-187,  and  observation  of  living  specimens.) 

8.  Does  the  leaf  determine  the  position  of  the  node,  or  the  node  the 
position  of  the  leaf  ? 

9.  Strip  the  leaves  from  a  twig  of  one  order  of  arrangement  and  replace 
them  with  foliage  from  a  twig  of  a  different  order;  for  mstance,  place 
basswood  upon  white  oak,  birch  upon  lilac,  elm  upon  pear,  honeysuckle 
upon  barberry,  etc.  Is  the  same  amount  of  surface  exposed  as  in  the 
natural  order? 

10.  What  disadvantage  would  it  be  to  a  plant  if  the  leaves  were  arranged 
so  that  they  stood  directly  over  one  another  ?     (169.) 

11.  Why  are  the  internodes  of  vigorous  young  shoots,  or  scions,  gen- 
erally so  long  ?     (150.) 

12.  If  the  upward  growth  of  a  stem  or  branch  is  stopped  by  pruning, 
what  effect  is  produced  upon  the  parts  below,  and  why  ?     (152,  153.) 

13.  Give  some  of  the  reasons  why  corn  grows  so  small  and  stunted  when 
sown  broadcast  for  forage?     (60,  63,  169.) 

14.  What  is  the  use  of  "chopping"  {i.e.  thinning  out)  cotton? 

II.    THE   VEINING   AND   LOBING    OF   LEAVES 

Material.  —  Leaves  of  any  monocotyl  and  dicotyl  will  show  the  dif- 
ference between  parallel  and  net-veining.  To  illustrate  the  palmate  and 
pinnate  kinds,  the  leaves  of  grasses  and  arums  may  be  used  for  monocotyls, 
and  for  dicotyls,  those  of  ivy,  maple,  grape,  elm,  peach,  cherry,  etc. ;  for 
division,  examine  lobed  and  compound  leaves  of  as  many  kinds  as  are 
attainable.    A  specimen  showing  each  kind  of  veining  should  be  placed  in 


THE   LEAF 


155 


coloring  fluid  a  short  time  before  the  lesson  begins.  The  leafstalks  of 
celery  and  plantain  are  excellent  for  showing  the  relation  between  the  leaf 
veins  and  vascular  system  of  the  plant. 

171.  Parallel  and  net  veining.  —  Compare  a  leaf  of  the 
wandering  Jew,  lily,  or  any  kind  of  grass,  with  one  of  grape, 
ivy,  or  willow.  Hold  each  up  to  the  light, 
and  note  the  veins  or  little  threads  of  woody 
substance  that  run  through  it.  Make  a  draw- 
ing of  each  so  as  to  show  plainly  the  direc- 
tion and  manner  of  veining.  Write  under  the 
first,  parallel-veined,  and  under  the  second, 
net-veined.  This  distinction  of  leaves  into 
parallel  and  net-veined  cor- 
responds with  the  two  great 
classes  into  which  seed-bear- 
ing plants  are  divided,  mon- 
ocotyls,  as  a  general  thing, 
being  characterized  by  the 
first  kind,  and  dicotyls  by 
the  second. 

172.  Pinnate  and  pahnate  veining.  — 
Next,  compare  a  leaf  of  the  canna,  calla  lily, 
or  any  kind  of  arum,  with  one  of  the  elm, 
peach,  cherry,  etc.  What  resemblances  do 
you  notice  between  the  two  ?  What  differ- 
ences? Which  is  parallel-veined  and  which 
is  net-veined  ?  Make  a  drawing  of  each,  and 
compare  with  the  first  two.  Notice  that  in 
leaves  of  this  kind,  the  petiole  is  continued 
in  a  large  central  vein,  called  the  midrib, 
from  which  the  secondary  veins  branch  off 
on  either  side  like  the  pinnae  of  a  feather; 
whence  such  leaves  are  said  to  be  pinnatehj, 
or  feather  veined,  as  in  Figs.  206,  207.  In  fig.  207.  — Pin- 
the  cotton,  maple,  ivy,  etc.,  on  the  other    lately      paraiici- 

•11  ri-        veined    loaf   of    calla 

hand,  the  petiole  breaks  up  at  the  base  01  the   my  (After  Gray). 


Fio.  205.  —  Par- 
allel-veined leaf  of 
lily  of  the  valley 
(Afte)-  Gray). 


Fig.  20G.  —  Net- 
veined  leaf  of  a  wil- 
low. 


156 


PRACTICAL  COURSE  IN  BOTANY 


Fig.    208.  — Palmately     net- 
veined  leaf  of  wild  ginger. 


leaf  (Fig.  208)  into  a  number  of  primary  veins  or  ribs,  which 
radiate  in  all  directions  like  the  fingers  from  the  palm  of  the 
hand ;  hence,  such  a  leaf  is  said  to  be  palmntely  veined. 
Net-veined  leaves  —  the  plantain 
(Fig.  209),  wild  smilax,  beech,  dog- 
wood —  are  sometimes  ribbed  in  a 
way  that  might  lead  an  inexperi- 
enced observer  to  confound  them 
with  parallel-veined  ones,  but  the 
reticulations  between  the  ribs  show 
that  they  belong  to  the  net-veined 
class. 

173.  Veins  as  a  mechanical  sup- 
port. —  Hold  up  a  stiff,  firm  leaf  of  any  kind,  like  the  mag- 
nolia, holly,  or  India  rubber,  to  the  light,  having  first  scraped 
away  a  little  of  the  under  surface,  and  examine  it  with  a  lens. 
Compare  it  with  one  of  softer  texture,  like 
the  peach,  maple,  or  clover.  In  which  are 
the  veins  the  closer  and  stronger?  Which 
is  the  more  easily  torn  and  wilted  ?  Tear  a 
blade  of  grass  longitudinally  and  then  cross- 
wise ;  in  which  direction  does  it  give  way 
the  more  readily  ?  Tear  apart  gently  a  leaf 
of  maple,  or  ivy,  and  one  of  elm  or  other 
pinnately  veined  plant;  in  which  direction 
does  each  give  way  with  least  resistance? 
What  would  you  judge  from  these  facts  as 
to  the  mechanical  use  of  the  veins  ? 

174.  Effect  upon  shape.  —  By  comparing 
a  number  of  leaves  of  each  kind  it  will  l^e  seen  that  the 
feather-veined  ones  tend  to  assume  elongated  outlines  (Figs. 
197, 207) ;  the  palmate-veined  ones,  broad  and  rounded  forms 
(Figs.  195,  208).  Notice  also  that  the  straight,  unbroken 
venation  of  parallel- veined  leaves  is  generally  accompanied  by 
smooth,  unbroken  margins,  while  the  irregular,  open  meshes 
of  net-veined  leaves  are  favorable  to  breaks  and  indentations. 


Fig.  209. —  Ribbed 
leaf  of  plantain. 


THE   LEAF  157 

175.  Veins  as  water  carriers.  —  Examine  a  leaf  from  a 
stem  that  has  stood  in  red  ink  for  an  hour  or  two.  Do  you 
see  evidence  that  it  has  absorbed  any  of  the  liquid?  Cut 
across  the  blade  and  examine  with  a  lens.  What  course  has 
the  absorbed  liquid  followed?  What  use  does  this  indicate 
for  the  veins,  besides  the  one  already  noted?  Observe  the 
point  of  insertion  on  the  stem,  and  examine  the  scar  with  a 
lens :  do  you  see  any  evidence  of  a  connection  between  the 
leaf  veins  and  the  fibro vascular  bundles  of  the  stem?  (Ill, 
125,  126.  Notice  where  and  how  the  veins  end.  Are  they 
of  the  same  size  all  the  way,  or  do  they  grow  smaller  toward 
the  tip?  Are  they  separate  and  distinct,  or  are  they  con- 
nected throughout  their  ramifications,  like  the  veins  and 
arteries  of  the  human  body  ?  How  do  you  know  ?  Do  you 
see  any  of  the  coloring  fluid  in  the  small  reticulations  be- 
tween the  veins?     How  did  it  get  there? 

176.  The  nature  and  office  of  veins. — We  learn  from  173 
and  175  that  the  veining  serves  two  important  purposes  in  the 
economy  of  the  leaf :  first,  as  a  skeleton  or  framework,  to  sup- 
port the  expanded  blade ;  and  second,  as  a  system  of  water 
pipes,  for  conveying  the  sap  out  of  which  its  food  is  manu- 
factured. In  other  words  the  veins  are  a  continuation  of  the 
fibrovascular  bundles  into  the  leaves,  by  means  of  which  the 
latter  are  put  in  communication  with  the  body  of  the  plant. 

177.  The  relation  between  veining  and  lobing.  —  Com- 
pare the  outline  of  a  leaf  of  maple  or  ivy  with  one  of  oak  or 
chrysanthemum.  Do  you  perceive  any  correspondence  be- 
tween the  manner  of  lobing  or  indentation  of  their  margins, 
and  the  direction  of  the  veins?  (Figs.  210,  211.)  To  what 
class  would  you  refer  each  one  ? 

The  lobes  themselves  may  be  variously  cut,  as  in  the 
fennel  and  rose  geranium,  thus  giving  rise  to  twice-cleft, 
thrice-cleft  (Fig.  212),  four-cleft,  or  even  still  more  in- 
tricately divided  blades. 

178.  Compound  leaves.  —  Compare  with  the  specimens 
just  examined  a  leaf  of  horse-chestnut,  clover,  or  Virginia 


158 


PRACTICAL  COURSE  IN  BOTANY 


(^. 


FiQ.    210.  —  Pinnately 
lobed  leaf  of  horse  nettle. 


Fig.  211.  —  Palmately 
lobed  leaf  of  grape. 


Fig.  212. 


-  Palmately  parted  leaf  of 
a  buttercup. 


Fig.  213.  —  Pin- 
nately compound  leaf 
of  black  locust. 


Fig.  214.  —  Palmately  com- 
pound leaf  of  horse-chestnut. 


Fig.  215. —  Pin- 
nately trifoliolate  leaf 
of  a  desmodium. 


Fig.  216.  — Pal- 
mately trifoliolate 
leaf  of  wood  sorrel. 


THE  LEAF  159 

creeper,  and  one  of  rose,  black  locust,  or  vetch.  Notice  that 
each  of  these  last  is  made  up  of  entirely  separate  divisions  or 
leaflets,  thus  forming  a  compound  leaf.  Notice  also  that  the 
two  kinds  of  compound  leaves  correspond  to  the  two  kinds  of 
veining  and  lobing,  so  that  we  have  palmately  and  pinnately 
compound  ones.  In  pinnate  leaves  the  continuation  of  the 
common  petiole  along  which  the  leaflets  are  ranged  is  called 

the  rhachis. 

Practical  Questions 

1.  In  selecting  leaves  for  decorations  that  are  to  remain  several  hours 
without  water,  which  of  the  following  would  you  prefer,  and  why: 
smilax  or  Madeira  vine  (BoussingauUia)  ;  ivy  or  Virginia  creeper ; 
magnoha  or  maple;   maidenhair  or  shield  fern  (Aspidium)?     (173.) 

2.  Would  you  select  very  young  leaves,  or  more  mature  ones,  and  why? 

3.  Can  you  name  any  parallel- veined  leaves  that  have  their  margins 
lobed,  or  indented  in  any  way  ? 

4.  Which  are  the  more  common,  parallel-veined  or  net-veined  leaves  ? 

5.  Why  do  the  leaves  of  corn  and  other  grains  not  shrivel  lengthwise  in 
withering,  but  roll  inward  from  side  to  side?     (173.) 

6.  Can  you  name  any  palmately  veined  leaves  in  which  the  secondary 
veins  are  pinnate  ?  Any  pinnately  veined  ones  in  which  the  secondary 
veins  are  palmate  ? 

7.  Lay  one  of  each  kind  before  you ;  try  to  draw  a  pinnate  leaf  with 
palmate  divisions.  Do  you  see  any  reason  now  why  these  so  seldom  occur 
in  nature? 

8.  Name  some  advantages  to  a  plant  in  having  its  leaves  cut-lobed  or 
compound.     (169.) 

9.  Mention  some  circumstances  under  which  it  might  be  advantageous 
for  a  plant  to  have  large,  entire  leaves.     (169;  Plate  9.) 

10.  How  would  the  floating  qualities  of  the  leaves  of  the  pond  lily  be 
affected  if  their  blades  were  cut-lobed  or  compound  ? 

11.  Do  the  leaves  of  the  red  cedar  and  arbor  vita3  contribute  to  their 
value  as  shade  trees  ? 

12.  Name  some  of  the  favorite  shade  trees  of  your  neighborhood ;  do 
they,  as  a  general  thing,  have  their  leaves  entire,  or  lobed  and  compound  ? 

13.  Which  of  the  following  are  the  best  shade  trees,  and  why:  pine, 
white  oak,  mimosa  (Albizzia),  sycamore,  locust,  horse-chestnut,  fir,  maple, 
linden,  China  tree,  cedar,  ash? 

14.  Which  would  shade  your  porch  best,  and  why :  cypress  vine, 
grape,  gourd,  morning-glory,  wistaria,  clematis,  smilax,  kidney  bean, 
Madeira  vine,  rose,  yellow  jasmine,  passion  flower  ? 


160  PRACTICAL  COURSE  IN  BOTANY 

ni.    TRANSPIRATION 

Material.  —  Leafy  twigs  of  actively  growing  young  plants.  Sun- 
flower, corn,  peach,  grape,  calla,  and  arums  in  general  transpire  rapidly; 
thick-leaved  evergreens  and  hairy  or  rough  species,  like  mullein  and  hore- 
hound  more  slowly.  For  Exp.  63,  small-leaved,  large-leaved,  and  thick- 
leaved  kinds  will  be  needed. 

Appliances.  —  Glass  jars  and  bottles  with  air-tight  stoppers ;  a  little 
vaseline,  oil,  gardener's  wax,  thread,  cardboard,  and  a  pair  of  scales. 

Experiment  62.  To  show  why  leaves  wither.  —  Dry  two  self- 
sealing  jars  thoroughly,  by  holding  them  over  a  stove  or  a  lighted  lamp 
for  a  short  time  to  prevent  "sweating."  Place  in  one  a  freshly  cut  leafy 
sprig  of  any  kind,  leaving  the  other  empty.  Seal  both  jars  and  set  them 
in  the  shade.  Place  beside  them,  but  without  covering  of  any  kind,  a 
twig  similar  to  the  one  in  the  jar.  Both  twigs  should  have  been  cut  at 
the  same  time,  and  their  cut  ends  covered  with  wax  or  vaseline,  to  prevent 
access  of  air.  Look  at  intervals  to  sec  if  there  is  any  moisture  deposited 
on  the  inside  of  either  jar.  If  there  is  none,  set  them  both  in  a  refrigerator 
or  cover  with  a  wet  cloth  and  allow  to  cool  for  half  an  hour,  and  then  ex- 
amine again.  In  which  jar  is  there  a  greater  deposit  of  dew  ?  How  do  you 
account  for  it  ?  Take  the  twig  out  of  the  jar  and  compare  its  leaves  with 
those  of  the  one  left  outside ;  which  have  withered  the  more,  and  why  ? 

Experiment    63.    To    measure    the    rate   at  which    water   is 

GIVEN  OFF  BY  LEAVES  OF  DIFFERENT  KINDS.  —  Fill  three  glaSS  VCSSCls  of 

the  same  size  with  water  and  cover  with  oil  to  prevent  evaporation. 
Insert  into  one  the  end  of  a  healthy  twig  of  peach  or  cherry;  into  the 
second  a  twig  of  catalpa,  grape,  or  any  large-leaved  plant,  and  into 
the  third,  one  of  magnolia,  holly,  or  other  thick-leaved  evergreen,  letting 
the  stems  of  all  reach  well  down  into  the  water.  Care  must  be  taken  to 
select  twigs  of  approximately  the  same  size  and  age,  since  the  absorbent 
properties  of  very  young  stems  are  more  injured  by  cutting  and  exposure 
than  those  of  older  ones.  All  specimens  should  be  cut  under  water  as 
directed  in  Exp.  58.  Weigh  all  three  vessels,  and  at  the  end  of  twenty- 
four  hours,  weigh  again,  taking  note  of  the  quantity  of  liquid  that  has  dis- 
appeared from  each  glass.  This  will  represent  approximately  the  amount 
absorbed  by  the  leaves  from  the  twigs  to  replace  that  given  off.  Which 
twig  has  lost  most?  Which  least?  Note  the  condition  of  the  leaves 
on  the  different  twigs;  have  they  all  al)sorl)ed  water  about  as  rapidly 
as  they  have  lost  it  ?  How  do  you  know  this  ?  Pluck  the  leaves  from 
each  twig,  one  by  one,  lay  them  on  a  flat  surface  that  has  been  previously 
measured  off,  into  square  inches  or  centimeters,  and  thus  form  a  rough 
pstiiflate  of  the  area  covere4  by  each  specinjen.    M^kc  the  best  estimate 


THE  LEAP  161 

you  can  of  the  number  of  leaves  on  each  tree,  and  calculate  the  number 
of  kilograms  of  water  it  would  give  off  at  that  rate  in  a  day. 

Experiment  04.  Through  what  part  of  the  leaf  does  the  water 
GET  out?  —  Take  some  healthy  leaves  of  tulip  tree,  grape,  tro])u'olum, 
or  any  large,  soft  kind  attainable.  Cover  with  vaseline  the  leafdalk  and 
2ipper  surface  of  one ;  the  stalk  and  under  surface  of  a  second ;  the  stalk 
and  both  surfaces  of  a  third,  and  leave  a  fourth  one  untreated.  Suspend 
all  four  in  a  dry  place  by  means  of  a  thread  attached  to  the  petioles  so 
that  both  surfaces  may  be  equally  exposed.  The  leaves  must  be  all  of 
the  same  species,  and  as  nearly  as  possible  of  the  same  age,  size,  and  vigor, 
and  care  must  be  taken  that  none  of  the  vaseline  is  rubbed  off  in  handling. 
Examine  at  intervals  of  a  few  hours.  Which  of  the  leaves  withers  soonest  ? 
Which  keeps  fresh  longest?  From  what  part  would  you  conclude,  judg- 
ing by  this  experiment,  that  the  water  escapes  most  rapidly  ? 

179.  Transpiration,  nutrition,  and  growth.  —  We  learn 
from  the  foregoing,  and  from  Exps.  58  and  59,  that  plants 
give  off  moisture  very  much  as  animals  do  by  perspiration. 
The  two  processes  must  not  be  classed  together,  however, 
for  they  are  physiologically  different.  The  action,  in  plants, 
is  called  transpiration.  It  is  usually  assumed  that  a  large 
amount  of  water  must  pass  through  the  plant  in  order  to 
bring  to  it  the  necessary  supply  of  food  material ;  but  since 
the  entrance  of  mineral  salts  is  brought  about  by  osmosis, 
conditioned  by  the  living  cells  of  the  root;  and  since  osmosis 
of  salts  may  take  place  in  a  direction  opposite  to  that  of  the 
greater  movement  of  water,  it  follows  that  the  entrance  of 
salts  is  independent  of  transpiration. 

Inasmuch,  however,  as  a  certain  amount  of  water  is 
necessary  to  bring  the  hving  cells  into  a  condition  of  turgor 
(7)  so  that  they  may  grow,  it  follows  that  there  is  a  relation 
between  transpiration  and  growth.  If  transpiration  exceeds 
absorption  for  any  length  of  time,  the  tissues  will  be  de- 
pleted of  their  moisture,  as  is  shown  by  the  wilting  of  crops 
in  dry,  hot  weather ;  and  if  the  unequal  movement  continues 
long  enough,  the  plant  will  die.  Hence,  a  knowledge  of  the 
laws  governing  this  important  function  is  necessary  to  all 
who  are  interested  in  cultivating  agricultural  products. 


162 


PRACTICAL  COURSE  IN  BOTANY 


i8o.   Magnitude    of    the  work   of    transpiration.  —  Few 

people  have  any  idea  of  the  enormous  quantities  of  water 
given  off  by  leaves.  It  has  been  calculated  that  a  healthy 
oak  may  have  as  many  as  700,000  leaves,  and  that  111,225 
kilograms  of  water  —  equal  to  about  244,700  pounds  —  may 
pass  from  its  surface  in  the  five  active  months  from  June 

to  October.  At 
this  rate  226 
times  its  own 
weight  may  pass 
through  it  in  a 
year,  and  it 
would  transpire 
water  enough 
during  that  time 
to  cover  the 
ground  shaded 
by  it  to  a  depth 
of  20  feetli 
Lawn  grass  gives 
off  water  at  such 
a  rate  that  a  va- 
cant lot  of  150  X 
50  feet,  if  well 
turfed,  would  be 
capable  of  trans- 
piring over  a  ton 
of  water  a  day.  Compare  these  figures  with  the  average  yearly 
rainfall  in  our  Gulf  States  — 53  inches,  approximately — and 
you  can  form  some  estimate  of  the  injury  done  to  a  growing 
crop  from  this  cause  alone.  The  moisture  is  drawn  from  the 
surface  by  shallow  rooted  weeds  (81)  and  dissipated  through 
the  leaves.  In  the  case  of  forest  trees  the  effect  is  different. 
Their  roots,  striking  deep  into  the  soil,  draw  up  water  from 
the  lower  strata  and  distribute  it  to  the  thirsty  air  in  summer. 


Fig.  217.  —  A  "weeping  tree,"  showing  the  effect  where 
absorption  exceeds  transpiration.  Notice  the  position  of 
the  tree  near  the  water  where  the  roots  have  unlimited 
moisture.    {After  France.) 


1  Marshall  Ward,  "  The  Oak.' 


THE   LEAF  163 

As  the  water  given  off  by  transpiration  is  in  the  form  of 
vapor,  it  must  draw  from  the  plant  the  amount  of  heat 
necessary  for  its  vaporization,  and  thus  has  the  effect  of 
making  the  leaves  and  the  air  in  contact  with  them  cooler 
than  the  surrounding  medium.  At  the  same  time  the  cool- 
ness and  moisture  of  the  air  tend  to  check  the  loss  by 
evaporation  from  the  surface  soil.  It  is  partly  to  this  cause, 
and  not  alone  to  their  shade,  that  the  coolness  of  forests  is 
due.  Measurements  at  various  weather  bureau  stations  in 
the  United  States  show  that  in  summer  the  temperature  of 
oak  woods  is  4°  C.  lower  during  the  day  than  in  the  open, 
and  as  much  higher  at  night.  In  a  beech  wood  in  Germany 
the  difference  between  the  forest  and  the  general  tempera- 
ture amounted  to  as  much  as  7°  C. 

Practical   Questions 

1.  Is  there  any  foundation  in  fact  for  the  accounts  of  "weeping  trees" 
and  "rain  trees"  that  we  sometimes  read  about  in  the  papers?  (180; 
Exp.  48.) 

2.  Can  you  explain  the  fact,  sometimes  noticed  by  farmers,  that  in 
wooded  districts,  springs  which  have  failed  or  run  low  during  a  dry  spell 
sometimes  begin  to  flow  again  in  autumn  when  the  trees  drop  their  leaves, 
even  though  there  has  been  no  rain?     (180;  Exp.  63.) 

3.  Other  things  being  equal,  which  would  have  the  cooler,  pleasanter 
atmosphere  in  summer,  a  well-wooded  region  or  a  treeless  one?     (180.) 

4.  Could  you  keep  a  bouquet  fresh  by  giving  it  plenty  of  fresh  air? 
(Exp.  62.) 

5.  Why  does  a  withered  leaf  become  soft  and  flabby,  and  a  dried  one 
hard  and  brittle?     (7;  Exp.  62.) 

6.  Why  do  large-leaved  plants,  as  a  general  thing,  wither  more  quickly 
than  those  with  small  leaves?     (Exp.  63.) 

7.  Is  the  amount  of  water  absorbed  always  a  correct  indication  of  the 
amount  transpired  ?    Explain.     (179.) 

8.  Explain  the  difference  between  the  withering  caused  by  excessive 
transpiration  and  the  shrinkage  of  cells  due  to  plasmolysis.  Are  both  of 
these  physiological  processes  ? 

9.  Why  is  it  best  to  trim  a  tree  close  when  it  is  transplanted  ?  (179, 
180.) 

10.  Why  should  transplanting  be  done  in  winter  or  very  early  spring, 
before  the  leaves  appear  ?     (180.) 


164  PRACTICAL   COimSP:    IN   BOTANY 

IV.    ANATOMY   OF   THE   LEAF 

Material.  —  For  study  of  the  epidermis,  leaves  of  the  white  garden 
lily  {Lilium  album)  are  best,  as  the  stomata  can  be  seen  on  their  lower 
surface  with  the  naked  eye.  Wandering  Jew,  Spanish  bayonet  {Yucca 
aloifolia),  anemone,  narcissus,  iris,  canna,  show  them  under  a  hand  lens, 
but  less  distinctly.  For  sections,  beet,  mustard,  and  beech  leaves  may 
be  used,  or  ready-mounted  specimens  obtained  of  a  dealer. 

A  compound  microscope  is  needed  for  a  minute  study  of  the  loaf 
structure. 

i8i.  Stomata.  —  It  was  shown  in  Exp.  64  that  the  water 
of  transpiration  escapes  most  rapidly,  as  a  general  thing,  from 
the  under  surface  of  leaves.  To  find  out  why  this  is  so,  a 
careful  study  of  the  epidermis  will  be  necessary.  For  this 
purpose  procure,  if  possible,  the  leaf  of  a  white  garden  lily 
{Lilium  album),  wandering  Jew,  Spanish  bayonet  {Yucca 
aloifolia),  anemone,  narcissus,  iris,  or  canna.  The  first- 
named  is  preferable,  as  the  transpiration 
pores  can  be  seen  on  it  with  the  naked  eye. 
Examine  the  under  surface  with  a  hand 
lens,  and  you  will  see  that  it  is  covered  with 
small  eye-shaped  dots  like  those  shown  in 
Figs.  218  and  219.     Strip  off  a  portion  of 

Figs.    218,    219.  —      ,  .  ,  •       ,      ,  ,    •  ^       t    ^ 

Stomata  of  white  lUy  the  cpidei'mis,  hold  it  up  to  the  light  on  a 
leaf:  218,  closed;  219,  pjepg  Qf  moisteued  glass,  and  they  can  be 

open.     {After  Gray.)        ^  . 

seen  quite  clearly  with  a  lens.  These  dots 
are  the  pores  through  which  the  water  vapor  escapes  in 
transpiration,  and  through  which  air  finds  its  way  into  the 
tissues  of  the  leaf.  They  are  called  stomata  (sing.,  stoma), 
from  a  Greek  word  meaning  "  a  mouth."  Look  for  stomata 
on  the  upper  epidermis  ;  do  you  find  any,  and  if  so,  are  there 
as  many  as  on  the  under  surface  ?  Do  you  see  any  relation 
between  this  fact  and  the  results  obtained  from  Exp.  64? 
Can  you  see  any  good  reasons  why  the  stomata  should  be 
placed  on  the  under  side  in  preference  to  the  upper  ?  Are  they 
as  much  exposed  to  excessive  light  and  heat,  or  as  liable  to 
be  choked  by  dust,  rain,  and  dew  here  as  on  the  upper  side  ? 


THE   LEAF 


165 


Fig.  220.  — a  small 
piece  of  the  under  epider- 
mis of  an  oak  leaf,  highly- 
magnified  to  show  the 
stomata,  g,  and  minute 
hairs,  h. 


182.  Distribution  of  stomata.  —  While  stomata  are  gen- 
erally more  abundant  on  the  under  side  of  leaves,  this  is  not 
always  the  case.  In  vertical  leaves,  like  those  of  the  iris, 
which  have  both  sides  equally  exposed  to  the  sun,  they  are 
distributed  equally  on  both  sides.  In  plants  like  the  water 
lily,  where  the  under  surface  lies  upon  the 

water,  they  occur  only  on  the  upper  side. 
Succulent  leaves,  as  a  general  thing,  have 
very  few,  because  they  need  to  conserve 
all  their  moisture.  Submerged  leaves 
have  none  at  all ;  why  ? 

183.  Minute  study  of  a  leaf  epidermis. 
—  Place  a  bit  of  the  lower  epidermis  of 
a  leaf  under  the  microscope,  and  examine 
with  a  high  power.  It  will  appear,  if  a 
monocotyl,  to  be  composed  of  long,  flat, 
rectangular  spaces  (Fig.  221) ;  if  the  leaf 
of  a  dicotyl  is  used,  they  will  be  more  or  less  irregular  (Fig. 
220),  with  the  outlines  fitting  into  each  other  like  the  tiling 

of  a  floor  or  the  blocks  of  a  Chinese  puzzle. 
These  spaces  are  the  cells  of  the  epidermis, 
and  the  lines  are  the  cell  walls.  Can  you 
find  any  of  the  cell  contents?  The  cell 
sap  is  not  often  visible;  do  you  see  the 
nuclei  ?  Can  you  give  a  reason  why  the 
epidermal  cells  are  so  thin  and  flat  ?  Be- 
tween some  of  the  cells  you  will  see  two 
kidney-shaped  bodies  placed  with  their 
concave  sides  together  so  as  to  leave  a 
lenticular  opening  between  them.  This 
is  a  stoma,  and  the  kidney-shaped  bodies 
(Figs.  218,  219)  are  guard  cells.  They 
are  given  this  name  because  they  open 
or  close  the  mouth  of  the  stoma.  If 
you  will  imagine  a  toy  balloon  made  in  the  form  of  a  hol- 
low ring,  like  the  tire  of  a  bicycle,  you  can  easily  see,  from 


Fig.  221.  —  Under 
epidermis  of  an  oat  leaf, 
showing  stomata. 


166         PRACTICAL  COURSE  IN  BOTANY 

Figs.  218,  219,  that  when  the  ring  is  strongly  inflated,  it 
will  expand,  and  in  enlarging  its  own  circumference,  will  at 
the  same  time  increase  the  diameter  of  the  opening  in  the 

center.  When  the  ex- 
pansive force  is  removed, 
it  collapses,  thus  closing, 
or  greatly  reducing,  the 
aperture. 

In  the  same  way  the 
guard  cells,  when  there 

Fig.  222.-Outline  of  a  stoma  of  hellebore  '^  abundance  of  Water  in 

in  vertical  section.     The  darker  lines  show  the  them,  expand,  thuS  OpCU- 

shape  assumed  by  the  guard  cells  when  the  stoma  •         fV,        f  fVi    f  fV> 

is  open  ;   the  lighter  lines,   when  the  stoma  is  l^^S  ^'^^  StOma  SO  tnat  me 

closed.  The  cavities  of  the  guard  ceUs  with  the  water  vapor  pasSCS  OUt 
stoma  closed   are  shaded,    and    are  distinctly 

smaller  than  when  the  stoma  is  open.  more  readily.      But  when 

there  is  a  dearth  of 
moisture,  or  when,  by  reason  of  chemical  action  in  the  soil, 
the  roots  fail  to  supply  it,  the  leaves  wilt,  the  guard  cells, 
losing  their  water,  collapse,  closing  the  pore,  and  transpira- 
tion is  thus  prevented  or  greatly  retarded.     (Fig.  222.) 

Sketch  a  portion  of  the  epidermis  as  it  appears  under  the  mi- 
croscope, labeling  the  parts.  If  stomata  can  be  found  in  both 
conditions,  make  sketches  showing  them  both  open  and  closed. 

184.  Internal  structure  of  a  leaf.  —  Roll  a  leaf  blade,  or 
fold  it  tightly  to  facilitate  cutting,  and  with  a  scalpel,  or  a  very 
sharp  razor,  cut  the  thinnest  possible  slice  through  the  roll. 
This  will  give  a  section  at  right  angles  to  the  epidermis. 
It  should  be  so  thin  as  to  appear  almost  transparent.  Put  a 
small  bit  of  a  section  in  a  drop  of  water  on  a  slide,  place  under 
the  microscope,  using  a  high  power,  and  look  for  the  parts 
shown  in  Fig.  223.  Notice  the  horizontally  flattened  cells  of  the 
upper  epidermis,  e,  and  of  the  lower  epidermis,  e' ;  also  the  ver- 
tically elongated  palisade  cells,  p,  filled  with  particles  of  green 
coloring  matter.  These  particles  are  the  chlorophyll  bodies, 
to  which  the  green  color  of  the  leaf  is  due.  They  are  the 
active  agents  in  the  manufacture  of  plant  food,  and  in  a  leaf 


THE   LEAF 


167 


removed  from  the  plant  during  the  day  time  and  viewed 
under  a  high  power,  the  chlorophyll  bodies,  on  treatment 

Fhv 


8Ch 


Fhv 

Fig.  223.  —  Transverse  section  through  a  leaf  of  beet:  e,  upper  epidermis;  e', 
lower  epidermis ;  st,  stoma  ;  a,  air  space ;  p,  palisade  cells ;  t,  collecting  cells ;  sch, 
spongy  parenchyma ;  i,  i,  intercellular  air  spaces;  Fbv,  section  of  a  vein  (fibrovascu- 
lar  bundle). 

with  iodine,  will  be  seen  to  contain  granules  of  starch  which 

they  are  in  the  act  of  elaborating.     The  collecting  cells,  t, 

receive   the  assimilated   product   from  the 

palisade  cells  and  pass  it  on   through  the 

spongy  parenchyma,  sch,  to  the  fibrovascular 

bundles.     Notice  how  much  more  abundant 

the  green  matter  is  in  the  upper  part  of  the 

leaf  than  in  the  lower ;  has  this  anything  to 

do  with  the  deeper  color  of  the  upper  surfaces 

of  leaves?     Notice  the  opening,  st, 

lower  epidermis;  do  you  recognize  it?    (See  1^;;^ ^^^ji^TTor! 

Fig.  222.)   It  is  a  stoma,  seen  in  vertical 

section.     Notice  the  intercellular  air  spaces, 

I,  I,  in  the  spongy  parenchyma,  and  the  much  larger  one,  a, 

just  behind  the  stoma.    Why  is  this  last  so  much  larger? 


Fig.  224.  — Chlo- 
m    the    rophyll    bodies    con- 


ination.       Magnified 
250  times. 


168  PRACTICAL  COURSE   IN   BOTANY 

Sketch  the  section  of  your  specimen  as  it  appears  under 
the  microscope.  It  will  perhaps  differ  in  some  details  from 
the  one  shown  in  the  figure,  but  you  can  recognize  and  label 
the  corresponding  parts.  Be  sure  that  your  drawing  repre- 
sents accurately  the  relative  size  and  shapes  of  the  different 
kinds  of  cells. 

It  is  in  the  upper  surface,  where  the  chlorophyll  particles 
abound,  that  the  manufacture  of  food  goes  on  most  actively, 
and  from  the  under  surface,  where  the  stomata  are  situated, 
that  transpiration  takes  place  and  air  and  other  gases  pass 
to  and  from  the  interior.  These  facts  have  important  bear- 
ings on  the  growth  and  external  characters  of  leaves. 

Practical  Questions 

1.  Explain  why  a  plant  cannot  thrive  if  its  stomata  are  clogged  with 
foreign  matter.     (179;  Exp.  64;  184.) 

2.  Mention  some  of  the  ways  in  which  this  might  happen.     (181.) 

3.  Why  must  the  leaves  of  house  plants  be  washed  occasionally  to  keep 
them  healthy?     (179,181.) 

4.  Why  is  it  so  hard  for  trees  and  hedges  to  remain  healthy  in  a  large 
manufacturing  town  ? 

V.     FOOD    MAKING 

Material.  —  A  sprig  of  pondweed,  mare's-tail  {Hippuris),  hornwort 
(Ceratophyllum),  marsh  St.-John's-wort  (Elodea),  or  other  green  aquatic 
plant ;  bean  or  tropseolum,  or  other  green  leaves  gathered  from  plants 
growing  in  the  sunshine ;  a  healthy  potted  plant ;  a  small,  fresh  cutting. 
Appliances.  —  A  shallow  dish  of  water  and  two  glass  tumblers  or  wide- 
mouthed  jars ;  a  bent  glass  or  rubber  tube ;  a  piece  of  black  cloth  or  paper ; 
a  half  pint  of  alcohol ;  iodine  solution ;  a  glass  funnel  or  a  long-necked 
bottle  from  which  the  bottom  has  been  removed. 

Experiment  65.  Is  there  any  relation  between  sunlight 
AND  THE  green  COLOR  OF  LEAVES  ?  —  Placc  a  seedling  of  oats,  or  other 
rapidly  growing  shoot,  in  the  dark  for  a  few  days,  and  note  its  loss  of 
color.  Leave  it  in  the  dark  indefinitely,  and  it  will  lose  all  color  and  die. 
Hence  we  may  conclude  that  there  is  some  intimate  connection  between 
the  action  of  light  and  the  green  coloring  matter  of  leaves. 

Experiment  66.  Do  leaves  give  off  anything  else  besides 
WATER  ?  —  Submerge  a  green  water  plant,  with  the  cut  end  uppermost,  in 


THE  LEAF 


169 


a  glass  vessel  full  of  water,  and  invert  over  it  a  glass  funnel,  or  a  long- 
necked  bottle  from  which  the  bottom  has  been  removed  as  directed  in  Exp. 
53.  Expel  the  air  from  the  neck  of  the  funnel  — 
or  bottle — by  submerging  and  corking  under  water 
so  as  to  make  it  air-tight.  Place  in  the  sunlight  and 
notice  the  bubbles  that  begin  to  rise  from  the  cut 
end  of  the  plant.  When  they  have  partly  filled  the 
neck  of  the  funnel,  remove  the  stopper  and  thrust 
in  a  glowing  splinter.  If  it  bursts  into  flame,  or 
glows  more  brightly,  what  is  the  gas  that  was  given 
off?     (Exp.  22.) 

As  oxygen  is  not  a  product  of  respiration,  some 
other  process  must  be  at  work  here,  during  which 
oxygen  is  set  free,  and  some  other  substance  used 
up.     (Exps.  24  and  25.) 

Experiment  67.    What  is  the  substance  taken 

IN    WHEN    OXYGEN    IS   GIVEN    OFF  ?  —  Fill    twO    glaSS 

jars,  or  two  tumblers,  with   water,   to  expel   the 

air,  and  invert  in  a  shallow  dish  of  water,  having 

first  introduced  a  freshly  cut  sprig  of  some  healthy 

green  plant  into  one  of  them.     Then,  by  means 

of  a  bent  tube,  blow  into  the  mouth  of  each  tumbler 

till  all  the  water  is  expelled  by  the   impure  air 

from  the  lungs.     Set  the  dish  in  the  sunshine  and 

leave  it,  taking  care  that  the  end  of  the  cutting  is  in 

the  water  of  the  dish.     After  forty-eight  hours  re-  oxygen  in  sunlight 

move  the  tumblers  by  running  under  the  mouth  of 

each,  before  lifting  from  the  dish,  a  piece  of  glass  well  coated  with  vaseline 

(lard  will  answer),  and  pressing  it  down  tight  so  that  no  air  can  enter. 
Place  the  tumblers  in  an  upright  position, 
keeping  them  securely  covered.  Fasten  a 
lighted  taper  or  match  to  the  end  of  a  wire, 
plunge  it  quickly  first  into  one  tumbler,  then 
into  the  other,  and  note  the  result.  What 
was  the  gas  blown  from  your  lungs  into  the 
Fig.    226.  —  Experiment    jars?     (Exps.  23,  24.)    Why  did  the  taper  not 

for  showing  that  leaves  absorb     go  out  in  the  second  jar?     What  had  become 

carbon  dioxide  from  the  at-       ^  ,,  ,         j-      •  i    o 

mosphere.  O^  <^he  carbon  dioxide  ? 

Experiment  68.    To  show  that  light 

IS  NECESSARY  FOR   A   PLANT  TO   ABSORB    CARBON   DIOXIDE    AND   GIVE   OFF 

OXYGEN.  —  Repeat  Exp.  66,  keeping  the  plant  in  a  dark  or  shady  place; 
do  you  see  any  bubbles?   Test  with  a  glowing  match;   is  any  oxygen 


Fig.  225.  —  Experi- 
ment showing  that 
green  plants  give   off 


170 


PRACTICAL  COURSE   IN  BOTANY 


formed  in  the  tube  of  the  funnel?  Move  back  into  the  sunlight  and 
leave  for  a  few  hours ;  what  happens  when  you  thrust  a  glowing  splinter 
into  the  tube  ? 

Experiment  69.     Is  any  food  product  found  in  leaves  ?  —  Crush 

a  few  leaves  of  bean,  sunflower,  or  tropa^olum,  and  soak  in  alcohol  until  all 

the  chlorophyll  is  dissolved  out.     Rinse  them  in  water,  and  soak  the 

leaves  thus  treated  in  a  weak  solution  of  iodine  for  a  few  minutes,  then 

wash  them  and  hold  them  up  to  the  light.     If 

there  are  any  blue  spots  on  the  leaves,  what  are 

you  to  conclude  ?     If  a  test  for  sugar  is  to  be 

made,  use  sap  pressed  from  fresh  leaves;   for 

oils  and  fats,  leaves   should  be  dried  without 

being  placed  in  alcohol. 

Experiment  70.      Has  the  presence  or 
absence  op  light  anything  to  do  with  the 
occurrence  of  starch  in  leaves  ?  —  Exclude 
the  light  from  parts  of  healthy  leaves  on  a  grow- 
ing plant  of  tropffiolum,  bean,  etc.,  by  placing 
patches  of  black   cloth  or  paper   over  them. 
FiG.227.  — Leaf  arranged   Leave  in  a  bright  window,  or  preferably  out  of 
with  a  piece  of  tin  foil  to  ex-  doors,  for  several  hours,  and  then  test  for  starch 
elude  light  from  a  portion  of   ^s  in  the  last  experiment ;   do  you  find  any  in 
the  surface.  u     i   j         ^    9 

the  shaded  spots  : 

Experiment  71.  Is  the  presence  of  air  necessary  for  the 
production  of  starch  ?  —  Cover  the  blades  and  the  petioles  of  several 
leaves  with  vaseline  or  other  oily  substance  so  as  to  exclude  the  air,  and 
after  a  day  or  two  test  as  before. 

185.  Influence  of  plants  on  the  atmosphere.  —  These 
experiments  show  that  leaves  cannot  do  their  work  without 
light  and  air.  The  particular  element  of  the  atmosphere 
used  by  them  in  the  process  of  food  making  is  carbon  dioxide. 
Their  action  in  absorbing  this  gas  and  giving  off  oxygen 
tends  to  counterbalance  the  opposite  action  of  respiration, 
decomposition,  and  combustion  of  all  kinds,  by  which  the 
proportion  of  it  in  the  atmosphere  tends  to  be  constantly 
increased.  In  this  way  they  help  to  regulate  the  quantity 
of  it  present  and  have  a  beneficial  effect  in  ridding  the  air  of 
one  soui'ce  of  mipurity. 


THE   LEAF  171 

i86.  Photosynthesis.  —  In  our  examination  of  the  internal 
structure  of  the  leaf,  the  chlorophyll  bodies  (184)  were  found 
to  contain  small  granules  of  starch  which  the  chlorophyll, 
imder  the  stimulus  of  light,  had  elaborated  as  a  nutriment  for 
the  plant  tissues.  Hence,  the  leaf  may  be  regarded  as  a 
factory  in  which  vegetable  food,  mainly  starch,  is  manufac- 
tured out  of  the  water  brought  up  from  the  soil,  and  the  carbon 
dioxide  derived  through  the  stomata  from  the  atmosphere. 
In  this  process  carbon  dioxide  (COg)  is  combined  with  water 
(HgO)  in  such  proportions  that  part  of  the  oxygen  is  returned 
to  the  surrounding  air.  This  is  a  fundamental  food-forming 
process  characteristic  of  green  plants,  and  can  take  place 
only  in  the  light.  For  this  reason  it  has  been  named  Photo- 
synthesis, a  word  which  means  "  building  up  by  means  of 
light,"  just  as  photography  means  "  drawing  or  engraving 
by  means  of  light." 

In  carrying  on  the  operation  of  photosynthesis,  sunshine 
is  the  power,  the  chlorophyll  bodies  the  working  machinery, 
carbon  dioxide  and  water  the  raw  materials,  and  starch  or  oil 
the  finished  product,  while  oxygen  and  the  water  of  trans- 
piration represent  the  waste  or  by-products. 

187.  How  the  new  combination  is  effected.  —  It  may 
seem  strange  that  a  gas  and  a  liquid  should  combine  to  make 
something  so  different  from  either  as  starch,  but  their  chemi- 
cal constituents  are  the  same  in  different  proportions.  Water 
is  made  up  of  2  parts  hydrogen  and  1  part  oxygen;  carbon 
dioxide,  of  1  part  carbon  and  2  parts  oxygen,  while  starch 
contains  carbon,  hydrogen,  and  oxygen,  in  the  ratios  of  6, 
10,  and  5,  respectively.  Hence,  by  taking  sufficient  quanti- 
ties of  water  and  carbon  dioxide  and  combining  them  in  the 
proper  proportions,  the  leaf  factory  can  turn  them  into 
starch.  If  we  use  the  letters  C,  H,  and  0,  to  represent  Car- 
bon, Hydrogen,  and  Oxygen,  respectively,  the  new  combina- 
tion of  materials  can  be  expressed  by  an  equation;  thus:  — 

water         carbon  dioxide  starch  by-products 

5(H20)     +     6(C02)     =     (CeHioOe)     +     6(02)     =     12(0). 


172         PRACTICAL  COURSE  IN  BOTANY 

The  water  not  used  up  in  the  process  is  given  off  as  a  waste 
product  in  transpiration,  while  the  oxygen  is  retui'ned  to  the 
air,  as  shown  by  Exp.  66.  This  equation  is  not  to  be  under- 
stood as  representing  the  chemical  changes  that  actually  take 
place  in  the  leaf.  These  are  too  complicated,  and  at  present 
too  imperfectly  known,  to  be  considered  here.  It  will  serve, 
how^ever,  to  give  a  fair  idea  of  the  final  result  from  the  process 
of  photosynthesis,  however  brought  about. 

Simple  as  the  operation  appears,  the  chemist  has  not,  as 
yet,  been  able  to  imitate  it.  He  can  analyze  starch  into  its 
original  constituents,  but  while  he  has  the  ingredients  at 
hand  in  abundance,  and  knows  the  exact  proportions  of  their 
combination,  it  is  beyond  his  power,  in  the  present  state  of 
our  knowledge,  to  put  them  together.  Hence,  both  man 
and  the  lower  animals  are  dependent  on  plants  for  this  most 
important  food  element.  The  so-called  factories  that  supply 
the  starch  of  commerce  do  not  make  starch  any  more  than 
the  miller  makes  wheat,  but  merely  separate  and  render 
available  for  use  that  already  elaborated  by  plants. 

1 88.  Proteins.  —  Foods  of  this  class  are  mainly  instru- 
mental in  furnishing  material  for  the  growth  and  repair  of 
the  tissues  out  of  which  the  bodies  of  both  plants  and  animals 
are  built  up.  They  embrace  a  great  variety  of  substances, 
but  their  chemical  nature  is  very  complex  and  very  imper- 
fectly understood.  Nitrogen  is  an  important  element  in 
their  composition,  whence  they  are  commonly  distinguished 
as  "  nitrogenous  foods."  Besides  nitrogen,  there  are  present 
carbon,  hydrogen,  oxygen,  and  sulphur,  and  traces  of  the 
mineral  salts  absorbed  from  the  soil  are  found  in  varying 
quantities  in  the  ash  of  different  proteins.  The  percentages 
in  which  these  ingredients  are  combined  and  the  processes 
concerned  in  their  formation  are  at  present  a  matter  of  pure 
hypothesis.  Botanists  are  not  agreed  even  as  to  whether 
they  are  made  in  the  leaf  or  in  some  other  part  or  parts  of 
the  plant,  though  the  weight  of  opinion  inclines  to  the  view 
that  their  construction  takes  place  in  the  leaf. 


TJl£i    LiI^JAF  173 

189.  The  activities  of  leaves.  —  As  there  are  only  4  parts 
of  CO2  to  every  10,000  parts  of  ordinary  free  air,  it  has  been 
estimated  that  in  order  to  supply  the  leaf  factory  with  the 
raw  material  it  needs,  an  active  leaf  surface  of  one  square 
meter  —  a  little  over  one  square  yard  —  uses  up,  during 
every  hour  of  sunshine,  the  COg  contained  in  1000  liters 
(1000  quarts,  approximately)  of  air.  Suppose  an  oak  tree 
to  bear  500,000  leaves,  each  having  a  surface  of  16  sq.  cm.,  or 
4  sq.  in.,  and  working  12  hours  a  day  for  6  months  in  the 
year;  you  will  then  have  some  idea  of  the  enormous  quantity 
of  air  that  passes  each  season  through  its  leaf  system.  Add 
to  this  the  almost  incredible  volume  of  water  transpired  in 
the  same  time  (180),  and  we  may  well  stand  amazed  at  the 
tremendous  activities  of  these  silent  workers  that  we  are  in 
the  habit  of  regarding  as  mere  passive  elements  in  the 
general  landscape. 

190.  The  economic  value  of  leaves.  —  Besides  their  im- 
portance as  sanitary  and  food-making  agencies,  leaves  have 
a  direct  commercial  value  as  food  products  in  the  hay  and 
fodder  they  supply  for  our  domestic  animals,  the  tea  and 
salads  with  which  they  provide  our  tables,  the  aromatic 
flavors  and  seasonings  contained  in  them,  and  the  drugs, 
medicines,  and  dyes  of  various  kinds  for  which  they  furnish 
the  ingredients. 

Practical  Questions 

1.  Why  do  gardeners  "bank"  celery?     (Exp.  65.) 

2.  Why  are  the  buds  that  si)rout  on  potatoes  in  the  cellar,  white  ?  (Exp. 
65.) 

3.  Why  does  young  cotton  look  pale  and  sickly  in  long-continued  wet 
or  cloudy  weather?     (Exp.  65.) 

4.  Why  do  parasitic  plants  generally  have  either  no  leaves  or  very 
small,  scalelike  ones?     (85,  186,  187.) 

5.  The  mistletoe  is  an  exception  to  this;  explain  why,  in  the  light  of 
your  answer  to  question  4. 

6.  Could  an  ordinary  nonparasitic  plant  live  without  green  leaves? 
(186,  187.) 

7.  Arc  abundance  and  color  of  foliage  any  indication  of  the  health  of 
a  plant?     (186,  187;  Exp.  65.) 


174  PRACTICAL  COURSE  IN  BOTANY 

8.  Is  the  practice  of  lopping  and  pruning  very  closely,  as  in  the  process 
called  "pollarding,"  beneficial  to  a  tree  under  ordinary  conditions ?  (186, 
189;  Exp.  63.) 

9.  Name  some  plants  of  your  neighborhood  that  grow  well  in  the  shade. 

10.  Compare  in  this  respect  Bermuda  grass  and  Kentucky  blue  grass ; 
cotton  and  maize;  horse  nettle  {Solanwn  Carolinense)  and  dandelion; 
beech,  oak,  red  maple,  dogwood,  pine,  cedar,  holly,  magnolia,  etc. 

11.  Name  all  the  aromatic  leaves  you  can  think  of ;  all  that  are  used  as 
food,  beverages,  drugs,  and  dyes. 

12.  What  is  the  use  of  aromatic  and  medicinal  leaves  to  the  plant  itself  ? 
(Suggestion:  Why  does  the  housewife  put  lavender  or  tobacco  leaves  in 
her  woolen  chest  ?) 

13.  Which  would  be  richer  in  nourishment,  hay  cut  in  the  evening  or 
in  the  morning,  and  why?     (54,  186;  Exp.  70.) 

14.  ]\Iention  three  important  sanitary  services  that  are  rendered  by  a 
tree  like  that  shown  in  plate  6  or  8.     (180,  185,  189.) 

15.  Name  some  of  the  plants  employed  in  the  manufacture  of  starch. 

VI.  THE  LEAF  AN   ORGAN   OF  RESPIRATION 

Material.  —  A  number  of  vigorous,  freshly  cut  green  leaves ;  a  liter 
or  two  (one  or  two  quarts)  of  expanding  flower  or  leaf  buds. 

Appliances.  —  Some  wide-mouthed  jars  of  one  or  two  liters'  capacity; 
two  small  open  vials  of  limewater. 

Experiment  72.  Do  leaves  give  off  carbon  dioxide  ?  —  Cover 
the  bottoms  of  two  wide-mouthed  jars  with  water  about  two  centimeters 
(1  inch)  deep.  Place  in  one  a  number  of  healthy  green  leaves  with 
their  stalks  in  the  water,  and  insert  among  them  a  small  open  vial  con- 
taining limewater.  In  the  other  jar  place  only  a  vial  of  limewater  in  the 
clear  water  at  the  bottom,  this  last  being  merely  to  make  the  conditions 
in  both  vessels  the  same.  Seal  both  tight  and  keep  together  in  the  dark 
for  about  48  hours,  and  then  examine.  In  which  jar  does  the  lime- 
water  indicate  the  greater  accumulation  of  CO2  ?  (It  may  show  a  sliglit 
milkincss  in  the  other  vessel  due  to  gas  derived  from  the  inclosed  air  and 
water.)  From  this  experiment,  what  process  would  you  conclude  has 
been  going  on  among  the  leaves  in  jar  No.  1  ?     (Exp.  25.) 

Experiment  73.  Is  the  exhalation  of  carbon  dioxide  accom- 
panied   BY  ANY   OTHER  CONCOMITANT  OF   RESPIR.\TION  ? In    ExpS.    24, 

25,  it  was  shown  that  respiration  is  accompanied  by  heat ;  hence,  if  the 
production  of  carbon  dioxide  by  the  leaf  is  due  to  this  cause,  it  should  be 
attended  by  the  evolution  of  heat.  To  find  out  wlicther  this  is  the  case, 
partly  fill  a  glass  jar  of  two  liters'  capacity  with  unfolding  leaf  buds  ar- 


THE   LEAF 


175 


Fig.  22S.  —  Arrange- 
ment of  apparatus  to 
show  that  heat  and  car- 
bon dioxide  are  given  ofif 
by  leaf  buds. 


ranged  in  layers  alternating  with  damp  cotton  bat- 
ting or  blotting  paper  (Fig.  228) ;  close  the  jar 
tightly  and  leave  from  12  to  24  hours  in  the  dark 
to  prevent  the  action  of  photosynthesis.  Then 
insert  a  thermometer  and  note  the  rise  in  tem- 
perature. If  a  lighted  taper  is  plunged  in,  it  will 
quickly  be  extinguished,  showing  that  respiration 
has  been  going  on. 

iQi.   Respiration  in  leaves.  —  We  see 

from  experiments  like  the  foregoing  that 
the  leaf,  besides  carrying  on  the  functions 
of  digestion,  photosynthesis,  and  trans- 
piration, is  also  an  active  agent  in  the 
work  of  respiration.  In  this  function 
oxygen  is  used  up  and  carbon  dioxide 
given  off,  just  as  in  the  respiration  of  animals;  but  the 
process  is  so  slow  in  plants  that  it  is  much  more  difficult 
to  detect  than  the  contrary  action  in  photosynthesis,  and  is, 
in  fact,  not  perceptible  at  all  while  the  latter  is  going  on, 
though  it  does  not  cease  even  then. 

But  while  the  leaf  is  the  principal  organ  of  respiration,  the 
process  is  carried  on  in  other  parts  of  the  plant  as  well, 
else  it  could  not  survive  during  the  leafless  months  of 
winter.  It  appears  to  be  most  active  at  night,  but  this  is 
only  because  it  is  not  obscured  then,  as  during  the  day,  by 
the  more  active  function  of  photosynthesis.  Indeed,  it  was 
for  a  long  time  supposed  that  plants  "  breathed  "  only  at 
night,  and  it  was  thought  to  be  unwholesome  to  keep  them 
in  a  bedroom.  It  is  now  known,  however,  that  respiration 
goes  on  at  all  times  and  in  all  living  parts  of  the  plant,  but 
the  quantity  of  oxygen  taken  in  is  so  small  from  a  hygienic 
point  of  view  that  it  may  be  disregarded. 

192.  Distinctions  between  respiration  and  photosynthesis. 
—  While  these  two  functions  are  contrasting  and  antipodal, 
so  to  speak,  in  their  action,  they  are  mutually  complemen- 
tary and  interdependent,  the  one  manufacturing  food  and  the 
other  using  it  up,  or  rather  marking  the  activity  of  those 


176  PRACTICAL  COURSE  IN  BOTANY 

life  processes  by  which  it  is  used  up.  The  difference  between 
them  will  be  made  clear  by  a  comparison  of  the  two  pro- 
cesses as  summarized  in  the  following  statement : 

Photosynthesis  Respiration 

Goes  on  only  in  sunlight  and  in  Goes  on  at  all  times  and  in  all 
the  green  parts  of  plants,  parts  of  the  plant. 

Produces  starch  and  sugar.  Releases  energy  (heat  and  wo.k- 

ing  power). 
Gives  off,  as  by-product,  oxygen.         Gives   off,   as  by-products,   CO3 

and  water. 
A  constructive  process,  in  which        A   destructive,    or   consumptive 
energy  is  used  up  to  make  food.  process,  in  which  food  is  used  up  in 

expending  energy. 

193.  Metabolism.  —  The  total  of  all  the  life  processes  of 
plants,  including  growth,  waste,  repair,  etc.,  is  summed  up 
under  the  general  term  metabolism.  It  is  a  constructive  or 
building-up  process  when  it  results  in  the  making  of  new 
tissues  out  of  food  material  absorbed  from  the  earth  and  air, 
and  the  consequent  increase  of  the  plant  in  size  or  numbers. 
But,  as  in  the  case  of  animals,  so  with  plants,  not  all  the 
food  provided  is  converted  into  new  tissue,  part  being  used 
as  a  source  of  energy,  and  part  decomposed  and  excreted 
as  waste.  In  this  sense,  metabolism  is  said  to  be  destructive. 
The  waste  in  healthy  growing  plants  is  always,  of  course,  less 
than  the  gain,  and  a  portion  of  the  food  material  is  laid  by 
as  a  reserve  store.  For  this  reason,  photosynthesis,  being  a 
constructive  process,  is  usually  more  energetic  than  respira- 
tion, which  is  the  measure  of  the  destructive  change  of 
materials  that  attends  all  life  processes. 

It  is  evident  also,  from  what  has  been  said,  that  growth  and 
repair  of  tissues  can  take  place  only  so  long  as  the  plant  has 
sufficient  oxygen  for  respiration,  since  the  energy  liberated 
by  it  is  necessary  for  the  assimilation  of  nourishment  by 
the  tissues. 

Thus  we  see  that  plants  are  dependent  on  air  not  only  for 
respiration,  but  for  nutrition,  and  none  of  their  life  pro- 
cesses can  be  carried  on  without  it. 


THE  LEAF 


177 


Practical  Questions 

1.  Can  a  plant  be  suffocated,  and  if  so,  in  what  ways?  (87,  193; 
Exps.  26,  27.) 

2.  The  i-oots  on  the  palm  shown  in  plate  3  are  not  drawing  any  sap 
from  it  as  parasites;  why  does  their  continued  growth  bring  about  the 
death  of  the  tree  ?     (87,193.) 

3.  Is  it  unwholesome  to  keep  flowering  plants  in  a  bedroom  ?  Leafy 
ones?     Why,  in  each  case ?     (191.) 

4.  Would  there  be  any  more  reason  for  objecting  to  the  presence  of 
flowers  by  night  than  by  day  ?     Explain.     (191.) 

5.  Why  is  respiration  much  less  marked  in  plants  than  in  anunals? 
(30,  31.) 


VII. 


THE    ADJUSTMENT    OF   LEAVES    TO   EXTERNAL 
RELATIONS 


Material.  —  A  potted  plant  of  oxalis,  spotted  medick,  white  clover, 
or  other  sensitive  species.  The  subject  is  better  suited  for  outdoor  ob- 
servation than  for  laboratory  work. 

Experiment  74.  To  show  that  leaves  adjust  themselves  to 
CHANGES  IN  INTENSITY  OF  LIGHT.  —  Keep  a  healthy  potted  plant  of  oxalis, 
white  clover,  or  spotted  medick  in 
your  room  for  observation.  Note 
the  daily  changes  of  position  the 
leaves  undergo.  Sketch  one  as  it 
appears  at  night  and  in  the  morning. 

In  order  to  determine  whether 
these  changes  are  due  to  want  of  light 
or  of  warmth,  put  your  plant  in  a  dark 
closet  in  the  middle  of  the  day,  with- 
out change  of  temperature.  After 
several  hours  note  results.  Transfer 
to  a  refrigerator,  or  in  winter  place 
outside  a  window  where  it  will  be  ex- 
posed to  a  temperature  of  about  5°  C.  (40°  F.)  for  several  hours,  and  see  if 
any  change  takes  place.  Next  put  it  at  night  in  a  well-lighted  room  and 
note  the  effect.  If  practicable,  keep  a  specimen  for  several  weeks  in  some 
place  where  electric  lights  are  burning  continuously  all  night,  and  watch 
the  results. 

Experiment  75.  To  show  that  the  fall  of  the  leaf  may  result 
FROM  OTHER  CAUSES  THAN  COLD  OR  FROST.  —  Wrap  some  leavcs  of  ailan- 
thus,  Kentucky  coffee  tree,  ash,  walnut,  or  hickory  in  a  damp  towel  and 


Figs.  229,  230.  —  Leaves  of  a  peanut 
plant :  229,  in  day  position ;  230,  in 
night  position. 


178  PRACTICAL  COURSE   IN  BOTANY 

keep  them  in  the  dark  for  several  days ;  the  leaflets  will  fall  away,  leaving 
a  clear  scar  like  those  on  winter  twigs. 

Experiment  76.  To  show  that  adjustments  to  temperature  may 
BE  made  by  chemical  MEANS.  —  Placc  a  small  twig  of  oleander,  laures- 
tinus,  or  other  broad-leaved  evergreen  in  a  5  to  10  per  cent  solution 
of  sugar,  and  transfer  it  at  the  end  of  a  few  days  to  a  temperature  of 
6°  to  8°  below  freezing.  On  comparison  with  a  similar  twig  that  has 
stood  for  the  same  length  of  time  in  pure  water,  it  will  be  found  to  possess 
a  greater  power  of  resistance  to  cold. 

194.  The  light  relation.  —  The  principal  external  con- 
ditions to  which  leaves  have  to  adjust  themselves  are  light, 
air,  moisture,  gravity,  temperature,  and  the  attacks  of  ani- 
mals. From  the  knowledge  of  their  work  and  function 
gained  in  the  preceding  sections,  it  will  be  clear  that  the  pri- 
mary relation  of  the  leaf  is  a  light  relation,  and  to  this,  first  of 
all,  it  must  adjust  itself. 

It  was  shown  in  Exps.  56  and  57  how  promptly  leaves  re- 
spond to  changes  in  the  direction  of  light, 
and  a  little  observation  (Exp.  74)  will  con- 
vince us  that  they  are  equally  sensitive  to 
changes  in  intensity  and  periodicity  of  illu- 
mination. 

195.   Phototropism,  —  The  movement  of 
plants  in  response  to  light  is  called  photo- 
tropism —  a  word   that   means   "  turning 
Fig.    2  31.  — a  toward  or  away  from  light."     It  includes 
plant  that  has  been   ^^  j^jj^^jg  ^f  jj  j^^  adjustments,  and  examples 

growing  near  an  open  ^  .  .        , 

window,  showing  the  of  it  are  to  be  met  with  everywhere  m  the 
lowa'^rrthe^Hght"''"''^  disposition  of  Icavcs  with  reference  to  their 
light  exposure. 
196.  Horizontal  and  vertical  adjustment.  —  Take  two 
sprigs,  one  upright,  the  other  horizontal,  from  any  convenient 
shrub  or  tree  —  and  notice  the  difference  in  the  position  of 
the  leaves.  Examine  their  points  of  attachment  and  see  how 
this  is  brought  about,  whether  by  a  twist  of  the  petiole  or  of 
the  base  of  the  leaf  blades,  or  by  a  half  twist  of  the  stem 
between  two  consecutive  leaves,  or  by  some  other  means. 


THE   LEAF 


179 


tl. — A  mosaic  of  in()()n->cc(l  l('a\(-~,  ^li..\\i[iL'   kI  u-iui 
(,Froin  Mo.  Botanical  Liani;.u  liep  t.) 


gilt  I'xposuri.'. 


180 


PRACTICAL  COURSE  IN  BOTANY 


Observe  both  branches  in  their  natural  position ;  what  part 
of  the  leaf  is  turned  upward,  the  edge  or  the  surface  of  the 
blade?  Change  the  position  of  the  two  sprigs,  placing  the 
vertically  growing  one  horizontal,  and  the  horizontal  one 
vertical.     "What  part  of  the  leaves  is  turned  upward  in  each  ? 


232  233 

Figs.  232,  233.  —  Adjustment  of  leaves  to  different  positions : 
232,  upright ;  233,  procumbent. 

197.  Leaf  mosaics.  —  Trees  with  horizontal  or  drooping 
branches,  like  the  elm  and  beech,  and  vines  growing  along 
walls  or  trailing  on  the  ground,  generally  display  their  foliage 
in  flat,  spreading  layers,  each  leaf  fit- 
ting in  between  the  interstices  of  the 
others  like  the  stones  in  a  mosaic, 
whence  this  has  been  called  the  mosaic 
arrangement.  (Plate  10.)  In  plants  of 
more  upright  or  bunchy  habit,  the 
leaves  are  placed  at  all  angles,  giving 
the  appearance  of  a  rosette  when  viewed 
from  above,  whence  this  is  called  the 
rosette  arrangement. 

A  variety  of  the  same  disposition  is 
seen  in  the  pyramidal  shape  assumed 
by  plants  with  large,  undivided  leaves 
like  the  mullein  and  burdock  (Fig.  237),  in  which  access  of 
light  is  secured  by  a  mutual  adjustment  between  the  size 
and  position  of  leaves,  the  upper  ones  becoming  successively 
smaller. 


Fig.  234.  —  Leaf  mosaic 
of  olm. 


THE   LEAF 


181 


198.   Heliotropism  — 

' '  turning  with  the  sun' ' — is 
the  name  given  to  the  daily 
movement  of  plants  like  the 
cotton  and  sunflower  in 
turning  their  leaves  or  their 


2:35  236 

Figs.  235,  236.  —  Horse-chestnut  leaves:  235,  leaf  rosette  seen  from  above; 
236,  the  same  seen  sidewise,  showing  the  formation  of  rosettes  by  the  lengthening 
of  the  lower  petioles. 

blossoms  to  face  the  sun.     If  you  live  where  cotton  is  grown, 

notice  the  leaves  in  a  field  about  ten  o'clock  on  a  bright 

sunny  morning,  and  again  from  the  same 

point  of  view  at  about  four  or  five  in  the 

afternoon.  Do  you  perceive  any  differ- 
ence in  their  general  dis- 
position? Watch  on  a 
cloudy  day  and  see  if 
any  change  takes  place. 
Find  out  by  observation 
whether  the  "  heliotrope  " 
of  the  hothouses  is  really 
heliotropic. 

199.  Adjustment 
against  too  great  intensity 
of  light.  —  Plants  fre- 
quently have  to  protect 
themselves  against  excess 
of   light  and  heat.     An 


Fig.    237.— Leaf 
oyramid  of  mullein. 


compass  plant,  rosin- 
weed  (Silphium  lacini- 
atum)  :  238,  seen  from 
the  east  ;  239,  soon 
from  the  south. 


182 


PRACTICAL  COURSE  IN  BOTANY 


interesting  example  of  this  kind  of  adjustment  is  furnished 
by  the  rosinweed,  or  compass  plant  (Silphium  lacinialum, 
Figs.  238,  239),  which  grows  in  the  prairies  of  Alabama  and 
westward,  where  it  is  exposed  to  intense  sunlight.  The 
leaves  not  only  stand  vertical,  but  have  a  tendency  to  turn 
their  edges  north  and  south  so  that  the  blades  are  exposed 
only  to  the  gentler  morning  and  evening  rays.  The  prickly 
lettuce  manifests  the  same  habit  in  a  less  marked  degree. 

200.  Night  and  day  adjustments.  —  These  are  move- 
ments in  resj)onse  to  changes  in  the  degree  of  illumination 
and  temperature,  as  evidenced  by  the  fact  that  they  become 
feeble  and  soon  cease  altogether  if  the  plant  is  kept  a  suffi- 
cient time  under  uniform  conditions  as  to  these  two  factors. 
(Exp.  74.)  They  are  called  ''  nyctitropic  "  or  sleep  move- 
ments, because  they  are  most  obvious  in  certain  plants  that 
undergo  periodic  adjustments  to  the  alternations  of  day  and 
night  suggestive  of  an  imaginary  likeness  to  the  sleep  of  ani- 
mals. Examples  are 
most  frequently  met 
with  among  members  of 
the  pea  family  {Legumi- 
noscB),  the  spurges 
( Euphorbiacece) ,  and  the 
sorrel  (Oxalis)  family. 
They  are  found  among 
other  species  also,  and 
indeed  are  much  more 
general  than  is  usually 
supposed,  most  plants 
showing  signs  of  them 
if  carefully  tested.  A 
simple  way  of  doing  this 
is  by  attaching  bristles  about  two  inches  long  to  the  tips  of 
two  leaves  on  opposite  sides  of  the  stem,  as  in  Figs.  240,  241, 
and  comparing  the  divergence  of  the  bristles  during  the  day 
and  at  nightfall.     In  this  way  a  change  of  position  in  the 


Figs.  240,  241.  — A  plant  of  the  guayule 
(Parthenium  nrgentntuni) ,  to  the  loaves  of  which 
indexes  have  been  affixed  to  show  their  day  and 
night  position:  240,  day  position;  241,  night 
position.  {From,  photographs  by  Prof.  F.  E. 
Lloyd.) 


THE   LEAF 


183 


leaves,  too  slight  to  attract  attention  otherwise,  will  be  made 
apparent.     The  positions  assumed  vary  in  different  plants, 


;^4..^-^ 

^ 

1 

f. 

n 

c; 

■'M 

^-"*^ 

^■i 

242 


243 


244 


Figs.  242-244.  —  Showing  the  movements  of  Amaranthus  Palmeri:  242,  243, 
position  at  sunrise  and  sunset  (heliotropic)  ;  244,  night  position  (nj'ctitropic)  half  an 
iiour  after  sunset.     (From  photographs  by  Prof.  F.  E.  Lloyd.) 

and  even  in  the  parts  of  the  same  compound  leaf ;  in  the 
kidney  bean,  for  instance,  the  common  petiole  turns  up  at 
night,  while  the  individual  leaflets  turn  down.  One  of  the 
common  pigweeds  {Amaranthus  Palmeri,  Figs.  242-244)  is 
heliotropic  in  the  day  time  and  nyctitropic  at  night. 


^Uii^ 

*">-*i^  -»» 

-J*^ 

'  r^  ^ 

?4S 


24! 


FiG,q.  245-250.  —  Wild  senna  (Cassia  tora),  showing  the  nyctitropic  adjustments 
of  its  leaves.  The  upper  figures  show  their  horizontal  arrangement ;  those  below, 
the  vertical:  245,  248,  position  of  the  leaves  at  9  a.m.;  246,  249,  at  3  p.m.;  247, 
250,  at  6.30  p.m.      (From  photographs  by  Prof.  F.  E.  Lloj'd.) 


The  very  striking  nyctitropic  adjustments  of  the  wild 
senna   {Cassia    tora)   photographed    by   Professor   Francis 


184  PRACTICAL  COURSE  IN  BOTANY 

E.  Lloyd  of  the  Alabama  Polytechnic  Institute  (Figs.  245- 
250),  though  obviously  influenced  by  the  sun,  are  not 
directed  toward  it  as  in  those  of  truly  heliotropic  plants. 

These  movements  are  common  also  among  flowers,  many 
of  them  having  regular  hours  for  opening  and  closing,  as  in- 
dicated b}^  such  names  as  "morning-glory"  and  "four- 
o'clock."  In  these  cases,  however,  other  causes  (277,  280) 
than  the  light  relation  must  be  taken  into  account. 

201.  Irritability  is  a  general  term  applied  to  the  power  in 
plants  of  receiving  and  responding  by  spontaneous  move- 
ments to  impressions  from  without.  In  its  widest  accepta- 
tion, irritability  includes,  besides  the  various  forms  of 
adjustment  described  in  this  section  and  the  next,  all  move- 
ments due  to  geotropism,  those  of  roots  seeking  air  and  mois- 
ture, the  revolution  of  twining  stems  and  tendrils,  the  circu- 
lation of  protoplasm  in  the  cell  —  any  movement,  in  short, 
that  is  made  in  response  to  an  impression  from  the  environ- 
ment is  a  manifestation  of  irritability.  It  may  be  of  various 
degrees,  but  is  possessed  to  some  extent  by  every  living  vege- 
table organism. 

The  term  is  usually  applied,  however,  more  especially  to 
those  obvious  and  pronounced  responses  made  by  plants  to 
their  surroundings,  as  exemplified  in  the  cases  just  given. 
Still  more  marked  instances  are  to  be  found  in  the  movements 
of  the  tentacles  of  insectivorous  plants,  and  the  sensitive 
leaflets  of  the  mimosa  that  close  at  the  slightest  touch.  The 
tendrils  of  the  passion  flower  are  said  to  appreciate  and 
respond  to  a  pressure  that  cannot  be  distinguished  even  by 
the  human  tongue,  and  many  i)lants  will  detect  and  respond 
to  the  ultra-violet  rays  of  light,  which  are  entirely  invisible 
to  man. 

This  faculty  of  irritability  among  plants  corresponds,  in  an 
imperfect,  rudimentary  way,  to  what  we  recognize  in  animals 
as  nervous  excitability.  By  this  it  is  not  meant  to  imply 
that  the  two  things  are  identical  in  their  ultimate  manifes- 
tations, though  we  may  regard  them  as  fundamentally  the 


THE  LEAF 


185 


same  in  that  they  are  both  to  be  referred  to  the  property 
inherent  in  protoplasm  of  responding  to  stimuH.  There  is 
no  indication,  however,  that  hritability  in  the  vegetable 
kingdom  is  accompanied  by  anything  like  consciousness  or 
volition,  or  that  plants  possess  any  power  of  initiative. 
While  the  movements  in  response  to  stimuli  are  in  many 
cases  eminently  adapted  to  a  purpose,  we  have  no  evidence 
of  a  controlling  power  behind  them.  The  movement  comes 
automatically  in  response  to  the  stimulus,  whether  the  effect 
at  the  moment  be  advantageous  or  the 
reverse. 

202.  Adjustments  in  relation  to 
moisture.  — -  These  adjustments  may 
be  —  (1)  To  guard  against  excess  of 
moisture ;  e.g.  glands  for  excreting  water 
and  salts ;  scales,  wax,  down,  etc.,  on 
the  surface  of  leaves.  These  may  serve 
also  for  protection  against  cold,  insects, 
excess  of  light  and  heat.  (2)  For  the 
conservation  of  moisture  ;  e.g.  the  rev- 
olute  leaf  margins  of  grasses  and  sand  plants  growing  along 
the  seashore ;  the  fleshy  leaves  of  stonecrops  and  purselanes; 
the  hard  epidermis  of  yuccas  and  aloes ;  the  scales,  scurf,  and 
down,  by  which  the  moisture  absorbed  from  the  soil  by  plants 

growing  in  dry  and  bar- 
ren places  is  prevented 
from  escaping  too 
rapidly  through  the 
stomata ;  the  leaf  cups 
and  holders  sometimes 
formed  by  winged 
petioles  and  clasping 
leaf  bases  for  retaining 
dew  or  rain  water. 
(3)  For  leaf  drainage, 
or    the    conduction    of 


Fig.  251.  —  Cross  sec- 
tions of  the  leaf  of  sand 
grass  :  a,  unrolled  in  its  or- 
dinary position ;  b  and  c, 
rolled  up  to  prevent  too 
rapid  transpiration. 


Fig.  252.— 
Winged  petiole  of 
Polymnia. 


Fig.  253. —  Water 
cups  of  Silphium  per- 
folialum. 


186 


PRACTICAL  COURSE  IN  BOTANY 


moisture,  by  means  of  grooves,  channels,  and  taper-pointed 
leaves,  which  act  as  natural  gutters  and  drain  pipes. 

203.  The  fall  of  the  leaf.  —  This  is,  in  effect,  an  adjust- 
ment to  change  of  temperature,  but  that  it  is  not  directly  due 
to  cold  is  shown  by  Exp.  75,  and  also  by  the  fact  that  leaves 
in  the  tropics  and  those  of  evergreens,  while  they  do  not  fall 
at  stated  periods  like  the  bulk  of  the  foliage  in  the  temperate 
zones,  are  cut  off  just  the  same  and  replaced  by  new  ones, 

whenever,  for  any 
reason,  they  are  un- 
able to  perform  their 
function.  In  cold 
climates  they  fall  at 
the  approach  of 
winter,  not  because 
the  frost  loosens 
them,  but  because 
the  roots  are  not  able 
to  absorb  enough 
moisture  to  supply 
them  with  material 
for  making  food. 
The  needles  and  the 
scale-leaves  charac- 
teristic of  evergreens 
in  cold  regions  are 
enabled  to  persist  indefinitely  by  reason  of  their  contracted 
surface.  This  prevents  the  dissipation  of  moisture  and  affords 
no  lodging  for  the  accumulations  of  sleet  and  snow  that 
would  otherwise  cumber  and  perhaps  break  the  boughs  with 
their  weight.  Trees  and  shrubs  that  shed  their  leaves  in  win- 
ter are  said  to  be  deciduous,  from  a  Latin  word  meaning  "  to 
fall."  Can  you  mention  some  advantages  of  the  deciduous 
habit  to  a  plant  with  broad,  expanded  leaves,  growing  in 
a  cold  climate? 

The  mechanical  means  by  which  the  leaf  fall  is  accom- 


FiG.  254.  —  Fallen  leaves.  Notice  how  they  cover 
the  ground  with  a  warm  mulch,  protecting  the  soil 
from  denudation,  and  the  roots  and  seeds  from  frost. 


THE  LEAF  187 

plished  is  through  the  growth  of  a  corky  layer  of  loose 
cells  that  forms  at  the  base  of  the  petiole  and  cuts  it  away 
from  the  stem,  leaving  a  smooth,  clean  scar.  Tear  some 
fresh  young  leaves  from  a  growing  twig  and  compare  the 
scars  with  those  on  a  winter  bough.  Do  you  see  any 
difference?  This  corky  layer  can  be  made  to  form  in 
some  plants  artificially,  by  depriving  them  of  working  ma- 
terial.    (Exp.  75.) 

204.  The  protection  of  winter-green  leaves.  —  A  great 
many,  perhaps  the  majority  of  broad-leaved  evergreens, 
bear  no  obvious  protection  against  cold,  while  a  large  pro- 
portion, such  as  chickweed,  violet,  fumitory,  groundsel 
{Senecio),  and  dead  nettle  {Lamium),  would  seem  peculiarly 
unfitted,  by  their  delicate  structure,  to  withstand  it.  But 
recent  investigations  by  the  Swedish  botanist,  Lidforss, 
have  shown  that  all  winter-green  leaves,  with  the  exception 
of  those  on  submerged  water  plants,  which  are  sufficiently 
protected  by  the  medium  in  which  they  live,  lose  their 
starch  in  winter  and  contain  instead  an  increased  percentage 
of  sugar.  The  same  is  true  of  other  vegetable  structures 
also,  where  starch  is  present,  such  as  roots,  stems,  tubers, 
and  winter  fruits  —  nuts,  haws,  persimmons,  and  the  like, 
which,  as  every  schoolboy  knows,  become  perceptibly  sweeter 
after  frost. 

The  presence  of  certain  substances,  of  which  sugar  is  the 
most  frequent,  enables  plants  to  withstand  a  greater  degree 
of  cold  than  they  could  otherwise  endure  (Exp.  76).  This 
effect,  as  shown  by  Lidforss's  experiments,  is  due  to  the 
action  of  sugar  in  counteracting,  or  retarding,  the  "  salting 
out  "  of  proteins  by  cold,  as  explained  in  33. 

As  sugar  is  readily  reconverted  into  starch  by  exposure  to 
a  moderately  high  temperature  for  even  a  few  days,  we  may 
find  here  an  explanation  of  the  fact  that  plants  which  have 
survived  the  prolonged  cold  of  winter  are  often  killed  by  a 
single  sharp  night  frost  following  a  few  warm  days  in  early 
spring,  before  the  tender  new  growth  has  appeared.     The 


188  PRACTICAL   COURSE   IN   BOTANY 

plant  suffers,  not  from  the  direct  effects  of  cold,  but  from 
the  warmth  preceding  it,  which  stimulated  the  transforma- 
tion into  starch  of  the  sugar  that  would  have  prevented  the 
loss  of  proteins.  On  the  same  principle  we  may  account  for 
the  puzzling  fact  that  the  sunny  southern  side  of  trees  and 
shrubs  usually  suffers  more  from  the  effects  of  sudden  frost 
than  the  shaded  and  colder  northern  face. 

In  apparent  conflict  with  this  reasoning  is  the  fact  that 
sugar  cane  and  the  sugar  beet  are  peculiarly  susceptible  to 
cold.  This,  however,  does  not  invalidate  the  premises  es- 
tablished by  Lidforss's  researches,  but  merely  emphasizes 
the  need  of  further  investigation,  w^hich  may  either  reconcile 
all  the  facts,  or  modify  their  interpretation. 

205.  The  colors  of  autumn  leaves.  —  These  are  due  to 
the  breaking  up  and  disappearance  of  the  chlorophyll  when 
the  leaf  factory  has  to  "  shut  down  "  for  want  of  raw  ma- 
terial to  work  with  (203).  It  is  closely  connected  with  the 
appearance  of  frost,  since  the  same  changes  of  temperature 
which  produce  frost  cause  the  cessation  of  sap  flow  that 
brings  about  the  disorganization  of  the  chlorophyll  and  the 
formation  of  various  pigments  derived  from  it.  Besides 
these,  leaves  may  contain  other  coloring  matters  that  are 
perceptible  only  when  the  chlorophyll  disappears ;  and  in 
the  sap  there  is  a  reddish  pigment  which  becomes  either  a 
very  bright  red,  or  a  dark  purplish  maroon,  from  the  effect 
of  chemicals  that  combine  with  it  in  the  leaves.  With  these 
coloring  materials  at  command  it  is  easy  to  see  how  the 
autumn  woods  can  assume  such  splendid  hues. 

Practical  Questions 

1.  How  would  you  explain  the  fact  that  the  outer  twigs  of  trees  generally 
are  the  most  leafy?     (99,  194;  Exps.  57,  74.) 

2.  Is  the  common  sunflower  a  compass  plant  ?    Is  cotton  ? 

3.  Are  there  any  such  plants  in  your  neighborhood  ? 

4.  Compare  the  leaves  of  half  a  dozen  shade-loving  plants  of  your  neigh- 
borhood with  those  of  as  many  sun-loving  ones ;  which,  as  a  general  thing, 
are  the  larger  and  less  incised  ? 


THE   LEAF  189 

5.  Give  a  reason  for  the  difference.     (169.) 

6.  Why  do  most  leaves  —  notably  grasses  —  v5url  their  edges  backward 
in  withering  ?     (182.) 

7.  What  advantage  is  gained  by  doing  this  ?     (202.) 

8.  Observe  such  of  the  following  plants  as  are  found  in  your  neighbor- 
hood, and  report  any  changes  of  position  that  may  take  place  in  their 
leaves  and  the  causes  to  which  such  changes  should  be  ascribed :  wood 
sorrel,  mimosa,  honey  locust,  wild  senna,  partridge  pea,  wild  sensitive  plant, 
redbud,  bush  clover,  Japan  clover,  Kentucky  coffee  tree,  sensitive  brier 
(Schrankia),  peanut,  kidney  bean. 

9.  Which  of  the  trees  named  below  shed  their  leaves  from  base  to  tip 
of  the  bough  (centripetally),  and  which  in  the  reverse  order:  ash,  beech, 
hazel,  hornbeam,  lime,  willow,  poplar,  pear,  peach,  sweet  gum,  elm,  syca- 
more, mulberry,  China  tree,  sumac,  chinquapin  ? 

10.  Account  for  the  fact  that  evergreen  trees  and  shrubs  have  generally 
thick,  hard,  and  shiny  leaves,  like  those  of  the  holly  and  magnolia,  or  scales 
and  needles,  as  the  cedar  and  pine.     (203.) 

11.  Why  do  many  plants  which  are  deciduous  at  the  North  tend  to  be- 
come evergreen  at  the  South  ?     (203.) 

12.  Why  are  evergreens  more  abundant  in  cold  than  in  warm  climates  ? 
(203.) 

13.  There  is  an  apparent  inconsistency  between  questions  11  and  12; 
can  you  reconcile  it  ?     (203.) 

14.  Why  is  it  more  important  to  protect  the  south  side  of  trees  against 
exposure  to  frost  than  the  northern  side?     (33,  204.) 

15.  Explain  why  peach  orchards  on  the  tops  and  northern  slopes  of  ele- 
vated areas  are  less  liable  to  have  their  fruit  destroyed  by  late  frost  than 
those  in  the  valleys  and  on  the  southern  slopes.     (33,  204.) 

VIII.   MODIFIED   LEAVES 

Material.  —  Get  from  a  florist  a  potted  plant  of  sundew,  Venus's- 
flytrap,  sarracenia,  or,  if  possible,  one  of  all  tliree,  and  keep  in  the  school- 
room for  observation.  The  subject  can  be  studied  best  in  a  well-stocked 
greenhouse,  if  one  is  accessible. 

2o6.  Modification  and  adaptation.  —  Modification  is 
structural  adjustment,  or  adaptation,  carried  so  far  as  to 
obscure  the  original  form  of  an  organ.  Its  true  nature, 
however,  can  generally  be  determined  by  some  of  the  tests 
mentioned  in  100. 

Examples  of  the  modification  of  leaves  to  do  the  work  of 


190 


PRACTICAL  COURSE  IN  BOTANY 


other  organs  have  ah-eady  been  noticed,  as  also  their  entire 
disappearance  in  certain  cases  (97,  101,  149)  and  replace- 
ment by  other  parts;  it  is 
unnecessary,  therefore,  to 
revert  to  this  branch  of  the 
subject  here. 

207.  Protective  modifica- 
tions. —  The  most  general 
protective  modifications 
that  leaves  undergo  are 
(1)  for  the  conservation  of 
moisture,  as  explained  in 
202,  and  (2)  for  protection 
against  animals.  Many  of 
the  adaptations  for  the 
former  purpose  serve  inci- 
dentally for  defense  against 
animals  also.  Spines,  hairs, 
scales,  sticky  exudations, 
water  holders,  clasping  and 
perfoliate  leaves  bar  the  way  to  crawling  insects ;  horny 
cuticles,  as  well  as  offensive  odors,  bitter  secretions,  and 


i'lG.    255.  —  Spearlike  leaves  of  Spanish 
bayonet. 


^ 


F 


i;5G 
FiG3.  256-258. 


257 


■  Protective  hairs  magnified  :  256,  mullein  ;  257,  cinque-foil 
258,  Shepherdia. 


poisonous  juices  warn   leaf -eating  cattle   and  bugs  away. 
These  devices  are  merely  protective,  however,  and  adapted 
to  a  passive  attitude  of  self-defense. 
2o8.   Insectivorous    leaves.  —  But    sometimes     a    plant 


THE   LEAF 


191 


becomes  the  aggressor,  and  instead  of  standing  on  the  defen- 
sive or  suffering  itself  to  be  quietly  devoured,  proceeds  to 
capture  and  devour  small  game  on  its  own  account,  and  in 
this  case,  the  leaf  sometimes  becomes  a  deadly  weapon  of 
destruction. 

209.  Pitcher  plants.  —  The  sarracenia,  or  trumpet  leaf, 
is  a  familiar  example  of  this  class.  The  lower  part  of  the 
leaf  blade  is  transformed 
into  a  hollow  vessel  for 
holding  water,  and  the 
top  is  rounded  into  a 
broad  flap  called  the 
lamina.  Sometimes  the 
lamina  stands  erect,  as 
in  the  common  yellow 
trumpets  of  our  coast 
regions,  and  when  this  is 
the  case,  it  is  brilliantly 
colored  and  attracts  in- 
sects (Fig.  259).  Some- 
times, as  in  the  parrot- 
beaked  and  the  spotted 
trumpet  leaf,  it  is  bent 
over  the  top  of  the  water 
vessel  like  a  lid,  and  the 
back  of  the  leaf,  near  the  foot  of  the  lamina,  is  dotted  with 
transparent  specks  that  serve  to  decoy  foolish  flies  away 
from  the  true  opening  and  tempt  them  to  wear  themselves 
out  in  futile  efforts  to  escape,  as  we  often  see  them  do  against 
a  window  pane. 

If  the  contents  of  one  of  these  leaves  are  examined  with  a 
lens,  there  will  generally  be  found  mixed  with  the  water  at  the 
bottom  the  remains  of  the  bodies  of  a  large  number  of  in- 
sects. The  hairs  on  the  outside  all  point  up,  toward  the 
rim  of  the  pitcher,  while  those  on  the  inside  turn  down, 
thus  smoothing  the  way  to  destruction,  but  making  return 


Fig.  259.  —  Yellow  trumpets  (Sarniccnia  flava). 
{From  the  Mo.  Botanical  Garden  Rcp't.) 


192 


PRACTICAL  COURSE  IN  BOTANY 


impossible  to  a  small  insect  when  once  it  is  ensnared. 
When  we  remember  that  these  plants  are  generally  found 
in  poor,  barren  soil,  we  can  appre- 
ciate the  value  to  them  of  the  ani- 
mal diet  thus  obtained. 

210.  Flytraps.  —  The  most  re- 
markable examples  of  insect-catch 
ing  leaves  are  the  Venus 's-fly trap, 
found  in  the  seacoast  region  of 
North  Carolina,  and  the  sundew 
{Drosera  rotundifolia) ,  common  on 
the  margins  of  sandy  bogs  and 
ponds.  The  latter  is  a  delicate, 
innocent-looking  little  plant,  and 
owes  its  poetic  name  to  the  dewlike 
appearance  of  a  shining,  sticky 
fluid  exuded  from  glands  on  its 
leaves,  which  glitter  in  the  sun  like  dewdrops.  It  is,  however, 
a  most  voracious  carnivorous  plant,  the  sticky  leaves  acting 
as  so  many  bits  of  fly  paper  by  means  of  which  it  catches  its 


Fig.  260.  —  Plant  of  sundew. 


263 


Figs.  261-263.  —  Leaves  of  sundew  magnified  :   261,  leaf  expanded  ;  262,  leaf 
closing  over  captured  insect ;   263,  leaf  digesting  a  meal. 


prey.  When  a  fly  has  been  trapped,  the  tentacles  close 
upon  it,  the  edges  of  the  leaf  curve  inward,  making  a  sort  of 
stomach,  from  the  glands  of  which  an  acid  juice  exudes  and 


THE   LEAP 


193 


digests  the  meal.  After  a  number  of  days,  varying  according 
to  the  digestibihty  of  the  diet,  the  blades  slowly  unfold  again 
and  are  ready  for  another  capture. 

The  bladderwort,  common  in  pools  and  still  waters  nearly 
everywhere,  has  its  petioles  transformed  into  floats,  while 


^1-4^- 


Fig.  264.  —  Bladderwort,  showing  finely  dissected  submerged  leaves 
bearing  bladders  for  capturing  animalculae. 

the  finely  dissected,  rootlike  blades  bear  little  bladders  which, 
when  examined  under  the  microscope,  are  found  to  contain 
the  decomposed  remains  of  captured  animalculaB. 


I>ractical  Questions 

1.  Can  you  find  any  kind  of  leaf  that  is  not  preyed  upon  l^y  something? 
If  so,  how  do  you  account  for  its  immunity  ? 

2.  Make  a  list  of  some  of  the  most  striking  of  the  protected  leaves  of 
your  neighborhood. 

3.  Wliat  is  the  nature  of  the  protective  organ  in  each  case  ? 

4.  For  protection  against  what  does  it  seem  to  be  sj^ecially  adapted  ? 

5.  Are  the  plants  in  your  list  for  the  most  part  useful  ones,  or  trouble- 
some weeds  ? 


194  PRACTICAL   COURSE   IN  BOTANY 

6.  Examine  the  leaves  of  the  worst  weeds  that  you  know  of  and  see 
if  these  will  help  in  any  way  to  account  for  their  persistency. 

Field  Work 

(1)  In  connection  with  Sections  I  and  II,  observe  the  effect  of  the  lob- 
ing  and  branching  of  leaves  in  letting  the  sunlight  through.  Notice  any 
general  differences  that  may  appear  as  to  shape,  margin,  and  texture  in  the 
leaves  of  sun  plants,  shade  plants,  and  water  plants,  and  account  for  them. 
Study  the  arrangement  of  leaves  on  stems  of  various  kinds,  with  reference 
to  the  size  and  shapes  of  leaves  and  their  light  relations.  Consider  the 
value  of  the  various  kinds  of  foliage  for  shade ;  for  ornament ;  as  producers 
of  moisture ;   as  food  ;   as  insect  destroyers,  etc. 

Make  a  special  study  of  the  twelve  principal  deciduous  trees  of  j'our 
neighborhood.  Compare  the  leaves,  bark,  and  branches  of  the  same 
trees  so  that  you  will  be  able  to  recognize  them  by  any  one  of  these  means 
alone. 

(2)  In  connection  with  Sections  III  and  V,  consider  the  effects  upon  soil 
moisture  of  transpiration  from  the  leaves  of  forest  trees  and  from  those 
of  shallow-rooted  herbs  and  weeds  that  draw  their  water  supply  from 
the  surface.  Consider  the  value  of  forests  in  protecting  crops  from  exces- 
sive evaporation  by  acting  as  wind  breaks.  Study  the  effect  of  the  fall  of 
leaves  upon  the  formation  of  soil.  In  any  undisturbed  forest  tract  turn  up 
a  few  inches  of  soil  with  a  garden  trowel  and  see  what  it  is  composed  of. 
Notice  what  kind  of  plants  grow  in  it.  Note  the  absence  of  weeds  and 
account  for  it.  Compare  the  appearance  of  trees  scattered  along  windy 
hillsides,  where  the  fallen  leaves  are  constantly  blown  away,  or  in  any 
position  where  the  soil  is  unrenewed,  with  those  in  an  undisturbed  forest, 
and  then  give  an  opinion  as  to  the  wisdom  of  hauling  away  the  leaves  every 
year  from  a  timber  lot. 

(3)  In  Section  VII,  observe,  in  different  kinds  of  leaf  mosaics,  the  means 
by  which  the  adjustment  has  been  brought  about  and  the  purpose  it  sub- 
serves. Make  a  list  of  plants  illustrating  the  two  habits.  Notice  the  form 
and  position  of  petioles  of  different  leaves,  and  their  effect  upon  light  ex- 
posure, drainage,  etc.,  and  the  behavior  of  the  different  kinds  in  the  wind. 
Look  for  compass  plants  in  your  neighborhood,  and  for  other  examples  of 
adjustment  to  heat  and  light.  Study  the  position  of  leaves  at  different 
times  of  day  and  in  different  kinds  of  weather  and  note  what  changes  occur 
and  to  what  they  are  due. 

Make  a  list  of  ten  plants  that  seem  to  you  to  have  best  worked  out  the 
problem  of  leaf  adjustment,  giving  the  reasons  for  your  opinion. 

Study  the  drainage  system  of  different  plants  and  olxscrve  whether  there 
is  any  general  correspondence  between  the  leaf  drainage  and  the  root  sys- 


THE   LEAF  195 

terns.  This  will  lead  to  intorosting  questions  in  regard  to  irrigation  and 
manuring.  Where  plants  are  crowded,  the  growth  of  both  roots  and 
leaves  is  complicated  with  so  many  other  factors  that  it  is  best  to  select 
for  observations  of  this  sort  specimens  growing  in  more  or  less  isolated 
situations. 

Notice  the  time  of  the  expansion  and  shedding  of  the  leaves  of  different 
plants,  and  whether  the  early  leafers,  as  a  general  thing,  shed  early  or  late ; 
in  other  words,  whether  there  seems  to  be  any  general  time  relation  be- 
tween the  two  acts  of  leaf  expansion  and  leaf  fall. 

(4)  Under  Section  VIII,  look  for  instances  of  modified  leaves ;  study 
the  nature  of  the  different  modifications  you  find,  and  try  to  understand 
their  meaning  and  object.  Make  a  collection  (a)  of  all  the  leaves  you  can 
find  modified  to  serve  other  than  their  normal  purposes ;  (6)  of  all  the 
organs  of  other  kinds  that  have  been  modified  to  serve  as  leaves ;  (c)  of 
all  the  modified  parts  of  leaves  —  stipules  and  petioles  —  that  you  can 
find.  Keep  the  collections  separate,  labeling  each  specimen  with  the 
name  of  the  plant  it  belongs  to,  what  part  it  is,  what  use  it  serves, 
when  and  where  found.  These  collections  need  not  be  made  individu- 
ally, but  by  the  class  as  a  whole  and  kept  for  the  use  of  the  school. 

Observe  also  (d)  the  differences  between  young  and  old  leaves  of  the 
same  kind,  and  the  leaves  of  young  and  old  plants  or  parts  of  plants  of  the 
same  kind ;  (e)  resemblances  between  young  leaves  belonging  to  plants  of 
different  species ;  (/ )  between  young  leaves  of  one  species  and  mature  ones 
of  one  or  more  different  species.  Make  a  collection  of  all  the  specimens  you 
can  find  illustrating  the  three  points  mentioned,  referring  each  to  its  proper 
head,  and  giving  the  name  and  relative  age  —  old  or  young  —  of  all  speci- 
mens collected. 


CHAPTER  VII.     THE   FLOWER 
I.     DISSECTION   OF   TYPES   WITH   SUPERIOR   OVARY 

Material.  —  For  monocotyls,  any  flower  of  the  lily  family,  such  as 
tulip,  dogtooth  violet  {Erythronium) ,  trillium,  star-of-Bethlehem,  yucca, 
bear's  grass,  and  the  like.  The  large  garden  lilies  make  particularly  good 
examples,  but  they  are  for  the  most  part  spring  bloomers.  For  autumn, 
spiderwort  (Tradescantia) ,  arrow  grass  (SagiUaria),  or  late  specimens  of 
colchicimi  and  tiger  lily  may  be  used.  Any  of  these  will  meet  the  essential 
conditions  of  the  analysis  given  in  the  text,  but  care  should  be  taken  not  to 
select  for  this  exercise  lily-like  flowers  of  the  iris  and  amaryllis  families, 
which  have  the  ovary  inferior. 

For  examples  of  hypogynous  dicotyls,  flax,  linden,  pinks,  corn  cockle, 
wood  sorrel,  poppies,  tomato  blossoms,  and  other  common  flowers  can 
usually  be  obtained  without  difficulty.  In  autumn,  the  geraniums  so 
largely  cultivated  for  ornament  will  meet  all  the  conditions  of  the  analysis. 
Specimens  of  the  cress  family  —  wallflower,  cabbage,  mustard,  turnip  — 
can  generally  be  found  every^vhere  and  at  all  seasons,  and  they  possess 
the  advantage  of  having  their  flowers  throughout  the  order  put  up  on  so 
nearly  the  same  pattern  that  a  description  of  one  species  will  answer,  even 
in  details,  for  the  rest. 

For  sympetalous  specimens  of  the  hypogynous  type,  hyacinth,  lily  of 
the  valley,  bearberry,  huckleberry,  or  other  equivalent  forms  may  be 
used. 

Appliances.  —  A  compound  microscope  may  be  needed  for  examining 
minute  objects,  such  as  pollen  grains  and  ovules;  but  for  all  other  pur- 
poses, a  good  hand  lens,  with  the  pupil's  ordinary  laboratory  equipment 
of  drawing-materials,  notebook,  and  dissecting  needles,  will  be  sufficient 
for  the  studies  outlined  in  this  and  the  four  succeeding  sections. 

211.  The  floral  envelopes.  —  Make  a  sketch  of  your 
specimen  flower  from  the  outside.  Is  it  solitary,  or  one  of  a 
cluster?  If  the  latter,  refer  to  160-162  and  tell  the  nature 
of  the  cluster.  Notice  the  color ;  is  it  conspicuous  enough 
to  attract  attention  or  not?  Can  this  have  anything  to  do 
with  its  clustered  or  solitary  position?  Label  the  head  of 
the  peduncle  that  supports  the  flower,  receptacle;   the  outer 

196 


THE   FLOWER 


197 


greenish  leaves,  sepals;  the  inner,  Ughter-colored  ones, 
petals.  The  sepals  taken  together  form  the  calyx,  and  the 
petals,  the  corolla.     Where  the  petals  and  sepals  are  all 


-§stig 


266 


267 


265 

Figs.  265-267.  —  Flower  of  a  monocotyl  (star-of -Bethlehem),  with  superior 
ovary  dissected  :  265,  entire  flower,  showing  the  different  sets  of  organs  :  pet, 
petals ;  sep,  sepals ;  sta,  stamens  ;  pist,  pistil ;  pcd,  peduncle  ;  266,  side  view  with 
all  the  petals  and  sepals  but  two  removed  to  show  order  of  the  parts  :  r,  recepta- 
cle ;  o,  ovary ;  sty,  style  ;  stig,  stigma  —  parts  composing  the  pistil ;  /,  filament ; 
a,  anther  —  parts  composing  the  stamen  ;  267,  cross  section  of  the  ovary  :  c,  c,  car- 
pels ;  ov,  ovules  ;  pi,  placenta. 

separate  and  distinct,  as  in  the  tulip  and  the  star-of-Bethle- 
hem,  the  corolla  is  said  to  be  polypeialous  and  the  calyx 
polysepalous,  words  meaning,  respectively,  many-petaled 
and  many-sepaled.     Monopetalous    and      monosepalous,   or 


268 


269 


Figs.  268-269. — Yucca  blossom  :  268,  external  view:  6r,  bract ;  p<f,  peduncle  ; 
r,  receptacle  ;  s,  sepal ;  pet,  petal ;  269,  vertical  section  :  ped,  peduncle  ;  br,  bract ; 
r,  receptacle  ;  per,  perianth  ;  sta,  stamen  ;  o,  ovary  ;  nty,  style  ;  stg,  stigma.  The 
last  three  parts  named  compose  the  pistil. 

sympetalous  and  synsepalous,  are  terms  used  to  describe  a 
condition  in  which  the  petals  or  sepals  are  all  united  into 
one,  as  in  the  morning-glory  and  lily  of  the  valley.     In  many 


198 


PRACTICAL  COURSE  IN  BOTANY 


flowers,  there  is  little  or  no  difference  between  the  two  sets  of 
organs.  In  such  cases  the  calyx  and  corolla  together  are 
called  the  perianth,  but  the  distinction  of  parts  is  always 
observed,  the  outer  divisions  being  regarded  as  sepals,  the 
inner  ones  as  petals.  These  two  sets  of  organs  constitute 
the  floral  envelopes,  and  are  not  essential  parts  of  the  flower, 
as  it  can  fulfill  its  office  of  producing  fruit  and  seed  without 
them.  Note  their  number,  mode  of  attachment  to  the 
receptacle,  and  how  they  alternate  with  each  other.  Re- 
move one  of  the  sepals  and  one  of  the  petals,  and  notice  any 
differences  between  them  as  to  size,  shape,  or  color.  Which  is 
most  like  a  foliage  leaf?  Hold  each  up  to  the  light  and  try 
to  make  out  the  veining.  Is  it  the  same  as  that  of  the  foliage 
leaves  ?  If  a  light-colored  flower  is  used,  examine  a  specimen 
that  has  stood  in  coloring  fluid.  How  many  of  each  set  are 
there  ? 

212.   The  essential  organs.  —  Next  sketch  the  flower  on 
its  inner  face,  labeling  the  appendages  just  within  the  petals, 

stamens,  and  the  central  organ 
within  the  ring  of  stamens, 
pistil.  These  are  called  essen- 
tial organs  because  they  are 
necessary  to  the  production  of 
fruit  and  seed.  Note  their 
mode  of  insertion,  three  of  the 
stamens  in  a  flower  like  the 
star-of-Bethlehem  alternating 
with  the  petals,  and  the  other 
three  with  these  and  with  the 
lobes  of  the  base  of  the  pistil. 
213.  The  stamens.  —  No- 
tice whether  the  stamens  are 
all  alike,  or  whether  there  are 
differences  as  to  size,  height, 
shape,  color,  etc.  Do  these 
differences,  if  there  are  any, 


270    271      272 


273 


274 


Figs.  270-274.  — Stamens:  270,  a 
typical  stamen  with  the  terminal  an- 
ther, b,  surmounting  the  filament,  a, 
and  opening  in  the  normal  manner 
down  the  outer  side  of  each  cell  ;  271, 
stamen  of  tulip  tree,  with  adnate  ex- 
trorse  anther  ;  272,  stamen  of  an  eve- 
ning primrose  ((Enothera)  with  versatile 
anther ;  273,  stamen  of  pyrola,  the 
anther  cells  opening  by  chinks  or  pores 
at  the  top  ;  274,  stamen  of  a  cranberry, 
with  the  anther  cells  prolonged  into  a 
tube  and  opening  by  a  pore  at  the  apex. 
(After  Gray.) 


THE  FLOWER  199 

occur  indiscriminately  and  without  order,  or  in  regular  suc- 
cession between  the  alternating  stamens  ?  Examine  one  of 
the  little  powdery  yellow  bodies  at  the  tip  of  the  stamens, 
and  see  whether  they  face  toward  the  pistil  or  away  from  it. 

Remove  one  of  the  stamens  and  sketch  as  it  api)ears  under 
the  lens,  labeling  the  powdery  yellow  body  at  the  top, 
anther,  and  the  stalklike  body  supporting  it,  filament.  Usu- 
ally the  filaments  are  threadlike,  whence  their  name,  but 
sometimes,  as  in  the  star-of-Bethlehem,  they  are  flattened 
and  look  like  altered  petals.  See  if  you  can  find  such  a  one. 
What  would  you  infer  from  this  fact  as  to  the  possible  origin 
of  the  stamens?     (100.) 

Notice  the  two  little  sacs  or  pouches  that  compose  the 
anther,  as  to  their  shape  and  manner  of  opening,  or  dehisc- 
ing, to  discharge  the  powder  ^^  ^^,.^^ 
contained  in  them.  This  /J  f\  ^^^  i  I 
powder  is  called  pollen,  and  %„,4ii/  ^(  W  \kJy 
will  be  seen  under  the  lens         275         276         277         278 

to    consist    of    Httle    yellow       ,    Figs.  275-278  -Forms of  poUen:  275. 

from  mimidus;  27b,  star  cucumber ;  277 
grams.      These  are  of  differ-       wUd  balsam  apple ;  278,  hibiscus.    (After 

ent  shapes,  colors,  and  sizes,      ^^"^•) 

in  different  plants,  and  their  surface  often  appears  beautifully 
grooved  and  striate  when  sufficiently  magnified.  Place  some 
of  the  pollen  under  the  microscope  and  draw  two  of  the 
grains,  with  their  markings.  In  the  hibiscus  and  others  of 
the  mallow  family,  they  are  large  enough  to  be  seen  with  a 
hand  lens. 

214.  The  pistil.  —  Remove  the  stamens  and  sketch  the 
pistil  as  it  stands  on  the  receptacle.  Label  the  round  or 
oval  enlargement  at  the  base,  ovary,  the  threadlike  appendage 
rising  from  its  center,  style,  and  the  tip  end  of  the  style, 
stigma.  In  some  specimens  the  style  may  be  very  short,  or 
wanting.  In  this  case  the  stigma  is  sessile,  and  the  pistil 
consists  of  stigma  and  ovary  alone.  If  the  stigma  is  lobed 
or  parted,  count  the  divisions  and  see  if  there  is  any  corre- 
spondencfc  between  them  and  the  number  of  petals  and  sepals, 


200 


PRACTICAL  COURSE  IN  BOTANY 


or  of  the  lobes  of  the  ovary.  Examine  the  tip  with  a  lens 
and  notice  the  sticky,  mucilaginous  exudation  that  moistens 
it.  Can  you  think  of  any  use  for  this  ?  If  not,  tou(!h  one  of 
the  powdery  anthers  to  it,  and  examine  it  again  with  a  lens. 
What  do  you  see?  Can  you  blow  or  dust  the  pollen  from 
the  stigma? 

215.  Pollination,  or  the  transfer  of  pollen  from  the  anther 
to  the  stigma,  is  a  matter  of  great  importance,  as  the  pistil 
cannot  develop  seed  without  it,  except  in  the  case  of  a  few 
plants  like  the  Alpine  everlasting,  some  species  of  meadow 
rue  {Thalidrum),  and  Alchemilla,  which  have  the  unusual 
faculty  of  perfecting  seeds  in  the  absence  of  pollen.  Note 
the  relative  position  of  pistils  and  stamens  and  see  if  it  is 
such  that  the  pollen  can  reach  the  stigma  without  external 
agency. 

216.  The  ovary.  —  Observe  the  shape  of  the  ovary,  and 
the  number  of  ridges,  or  grooves,  that  divide  the  surface. 

Select  a  flower  which  has  begun  to 
wither,  so  that  the  ovary  is  well 
developed,  cut  a  cross  section  near 
the  middle,  and  try  to  make  out  the 
number  of  locules,  or  internal  divi- 
sions. Do  you  perceive  any  corre- 
spondence in  number  between  these 
and  the  ridges  or  lobes  outside  (Fig. 
280)  ?  Between  them  and  the  lobes 
of  the  stigma?  The  walls  that 
inclose  the  cavities  of  the  ovary 
are  called  carpels,  and  the  ridges  or 
depressions  that  mark  their  point 
of  union  on  the  outside  are  the 
sutures,  or  seams.  The  little  round 
bodies  in  the  locules,  as  the  compartments  of  the  ovary  are 
called,  are  the  ovules,  which  will  later  be  developed  into  seeds. 
Their  place  of  attachment  is  the  placenta.  If  they  are 
attached  to  the  walls  of  the  carpels  (Fig.  281),  the  placenta 


-^    r 

279  280 

Figs.  279,  280.  — Ovarj-  of 
yucca,  a  hypogynous  mono- 
cotyl,  dissected :  279,  vertical 
section  ;  oz;,  ovules  ;  280,  diagram 
of  a  horizontal  section  of  the 
same,  enlarged,  showing  the 
three  carpels  and  six  locules  ; 
ds,  dorsal  sutures ;  vs,  ventral 
sutures ;  ov,  ovules ;  pi,  pla- 
centa. 


THE   FLOWER 


201 


281  282  283 

Figs.  281-283.  — Different  kinds  of  placenta  : 
281,  parietal;  282,  central  and  axial;  283,  free 
central.  281  and  282  are  horizontal  sections  ;  283, 
vertical. 


is  parietal;  if  to  a  central  axis  formed  by  the  edges  of  the 
carpels  projecting  inwards  (Fig.  282),  it  is  central  and  axial ; 
if  instead  of  being  attached  to  the  carpels,  the  ovules  are 
borne  on  a  projection  from  the  receptacle,  the  placenta  is  a 
free  central  one  (Fig.  283).  If  your  cross  section  shows  a 
central  placenta,  make 
a  vertical  cut  down  to 
the  receptacle  and  find 
out  whether  it  is  free, 
or  axial.  What  ap- 
pears to  be  the  prmiary 
office  of  the  ovary? 
Make  an  enlarged 
sketch  of  your  speci- 
men in  both  vertical  and  horizontal  section,  labeling  correctly 
all  the  parts  observed. 

217.  Numerical  plan.  —  Make  a  horizontal  diagram 
of  the  plan  of  the  whole  flower,  after  the  model  given  in 
Fig.  284,  showing  the  order  of  attachment  of  the  different 
cycles,  —  sepals,  petals,  stamens,  and  pistils,  —  the  number 
of  organs  in  each  set,  and  their  mode  of  alternation  with  the 
organs  of  the  other  cycles.  Notice  that  the 
parts  of  each  set  are  in  threes,  or  multiples 
of  three.  This  is  called  the  numerical  plan 
of  the  flower,  and  is  the  prevailing  number 
among  monocotyls.  It  is  expressed  in  bo- 
FiG  284  —  Hori-  ^auical  language  by  saying  that  the  flower  is 
zontai  diagram  of  a    tri7nerous,   a  word   meaning  measured,  or 

flower  of  the  lily  kind.       t     •  i     i       <v     •     i  j.        e  .1 

The  dot  represents  dividcd  off,  luto  parts  of  three, 
the  growing  axis  of  218.  Vertical  order.  —  Next  make  a  ver- 
tical diagram  of  your  specimen  after  the 
manner  shown  in  Fig.  269,  and  note  carefully  that  the  ovary 
stands  above  the  other  organs  (this  is  true  of  all  the  lily 
family),  and  is  entirely  separate  and  distinct  from  them.  In 
such  cases  the  ovary  is  said  to  be  free,  or  superior,  and  the 
other  organs  inferior,  or  hypogynous,  a  word  meaning  "in- 


202  PRACTICAL  COURSE   IN  BOTANY 

serted  under  the  pistil. ' '     These  terms  should  be  remembered, 
as  the  distinction  is  an  important  one  in  plant  evolution. 

219.  Summary  of  observations.  —  In  the  flower  just  ex- 
amined, we  found  that  there  were  four  sets  of  floral  organs 
present  —  sepals,  petals,  stamens,  and  pistil ;  that  the  indi- 
vidual organs  in  each  set  were  alike  in  size  and  shape ;  that 
there  were  the  same  number,  or  multiples  of  the  same 
number  of  parts  in  each  set,  and  that  all  the  parts  of  each  set 
were  entirely  separate  and  disconnected,  the  one  from  the 
other,  and  from  those  of  the  other  cycles.  Such  a  flower  is 
said  to  be  :  — 

Perfect,  that  is,  provided  with  both  kinds  of  organs  essen- 
tial to  the  production  of  seed  —  stamens  and  pistil. 

Com-plete,  having  all  the  kinds  of  organs  that  a  flower  can 
have:  viz.  two  sets  of  essential  organs,  and  two  sets  of 
floral  envelopes. 

Symmetrical,  having  the  same  number  of  organs,  or  mul- 
tiples of  the  same  number,  in  each  set. 

Regular,  having  all  the  parts  of  each  set  of  the  same  size 
and  shape,  as  in  the  wild  rose  and  bellflower,  or  if  different, 
arranged  in  regular  order  or  pairs,  so  that  there  will  be  a 
correspondence  between  the  two  sides  of  the  flower,  as  in  the 
violet,  sweet  pea,  sage,  and  larkspur.  For  convenience,  the 
two  kinds  may  be  distinguished  as  complete  and  bilateral 
regularity,  respectively. 

The  opposites  of  these  terms  are :  imperfect,  incomplete, 
asymmetrical  or  unsymmetrical,   and  irregular. 

Note  that  regularity  refers  to  form,  symmetry  to  number 
of  parts,  and  that  a  flower  may  be  perfect  without  being 
complete. 

220.  Dissection  of  a  typical  dicotyl  flower.  —  (Poppy, 
flax,  pink,  tomato,  linden,  etc.,  can  be  substituted  for  the 
specimen  used  in  the  text.)  Gently  remove  the  sepals  and 
petals  from  a  wallflower,  stock,  mustard,  or  other  cress 
flower,  lay  them  on  the  table  before  you  in  exactly  the  order 
in  which  they  grew  on  the  stem,  and  sketch  them.     How 


THE  FLOWER 


203 


many  of  each  are  there,  and  how  do  they  alternate  with  one 
another?     Sketch  the  pistil  and  stamens  as  they  stand  on 


a 


287 


Figs.  285-288. — A  flower  of  the  cress  family  :  285,  side  view  ;  286,  view  from 
above  ;  287,  diagram  of  parts  :  p,  petals  ;  s,  sepals  ;  st,  stamens  ;  pi,  pistil ;  d,  claw 
of  petal ;  +,  +,  position  of  the  missing  stamens  ;  288,  pistil  and  stamens,  enlarged. 
(After  Gray.) 

the  receptacle ;  how  many  of  the  latter  are  there  ?  Notice 
that  two  of  the  six  are  outside  and  a  little  below  the  others, 
alternate  with  the  petals,  while  the  other  four  stand  opposite 
them,  as  is  natural,  if  they  were  alternating  with  another 
ring  of  stamens  between  themselves  and  the  corolla.  Put  a 
dot  before  two  of  the  sepals  in  your  first  drawing  to  indicate 
the  position  of  the  two  outer  stamens,  and  a  cross  before 
the  other  two  to  show  where  stamens  are  wanting  to  com- 
plete the  symmetry  of  this  set,  as  in  Fig.  287.  When  parts 
necessary  to  complete  the  plan  of  a  flower  are  wanting,  as 
in  this  case,  they  are  said  to  be  obsolete,  suppressed,  or 
aborted.  Place  dots  before  the  petals  to  represent  the  other 
four  stamens.  Sketch  one  of  the  anthers  as  it  appears 
under  a  lens,  showing  the  arrow-shaped  base,  and  the 
mode  of  attachment  to  the  filament.  Is  it  such  that  the 
pollen  can  reach  the  stigma  without  external  agency  ?  In 
what  manner  do  the  anthers  open  to  discharge  their  pollen  ? 
Are  the  anthers  and  stigma  mature  at  the  same  time? 
Remove  all  the  stamens  from  a  flower  and  sketch  the  pistil, 
showing  the  long,  slender  ovary,  the  very  short  style,  and  the 


204 


PRACTICAL  COURSE   IN   BOTANY 


capitate  (that  is,  round  and  knoblike)  stigma.     Make  cross 
and  vertical  sections  of  one  of  the  older  pistils  lower  down 

on  the  stem.  How  many 
ovules  does  it  contain? 
How  are  they  attached  ? 
Represent  the  position 
of  the  pistil  by  a  small 
circle  in  the  center  of 
your  sketch  of  the  sep- 
arate parts.  You  have 
now  a  complete  ground 
plan  of  the  flower.  Dia- 
gram a  vertical  section, 
as  in  Fig.  289,  showing 
the  position  of  the  ovary 
with  reference  to  the 
other  parts,  and  report 


Fig.  289.  —  Section  of  a  tomato  flower,  show- 
ing the  hypogynous  arrangement :  ex,  calyx  ; 
c,  corolla  ;  s,  stamens  ;  p,  pistil  ;  o,  ovary,  st, 
stigma.     (Twice  natural  size.) 


in  your  notebook  as  to  the  following  points 


Numerical  plan 

Symmetry 

Regularity  (complete  or  bilateral) 


Presence  or  absence  of  parts 
Union  of  parts 
Position  of  ovary 


II.     DISSECTION    OF  TYPES   WITH   INFERIOR    OVARY 

Material.  —  For  monocotyls  :  in  spring  and  early  summer,  iris,  snow- 
flake,  freesia,  crocus,  narcissus,  daffodil,  can  be  used ;  in  autumn,  gladiolus, 
blackberry  lily,  fall  crocus,  star  grass  (Hypoxys).  For  dicotyls  :  in  spring, 
flowers  of  apple,  pear,  quince,  gooseberry,  squash,  gourd,  melon  (with  both 
male  and  female  flowers) ;  in  late  summer  and  autumn,  fuchsia,  evening 
primrose  {(Enolhera),  willow-herb  {Epilobium). 

221.  Study  of  a  monocotyl  flower.  —  Compare  with  the 
specimens  examined  in  the  last  section,  a  narcissus,  snow- 
flake,  or  iris  flower.  What  difference  do  you  notice  in  the 
position  of  the  ovary  ?  Would  you  call  it  inferior  (below  the 
other  parts)  or  superior  (above  them)  ?  How  was  it  in  the 
lily  and  the  hyacinth?  If  your  specimen  is  an  iris,  notice 
that  it  is  sessile  in  the  axil  of  a  large  bract  called  a  spathe, 


THE   FLOWER 


205 


which  conceals  the  lower  part  of  the  flower.     Remove  the 

spathe  and  observe  that  the  lower  part  of  the  perianth  is 
united  into  a  long,  narrow  tube,  from 
the  top  of  which  the  sepals  and  petals 
extend  as  long,  curving  lobes. 

222.  Arrangement  of  parts.  — 
Sketch  the  out- 
side of  the  flower, 
labeling  the  ob- 
long, three-lobed 
enlargement  at 
the  base,  ovary; 
the  prolongation 
above  it,  tube  of 
the  perianth;  the 
three  outer  lobes 
with  the  broad 
sessile  bases, 
sepaZs;  the  others, 
with    their  bases 

narrowed  and  bent  inward,  petals.     Now  turn  the  flower  over 

and  sketch  the  inside,  labeling  the  three  large,  petal-like  expan- 
sions in  the  center, 

stigmas.     Do  you 

see  any  stamens  ? 

Remove    one    of 

the    sepals     and 

look    under     the 

stigma;  what  do 

you    find    there  ? 

Notice   the   little 

honey  pockets  at 

the    foot    of    the 

stamen.    Run  the 

head  of  your  pencil  into  them  and  see  what  would  happen 

to  the  head  of  an  insect  probing  for  honey. 


Fig.  290.  —  Iris  flower: 
sp,  spathes  ;  s,  sepals  +  p, 
petals  =  perianth. 


-  Vertical 
section  of  iris  flower: 
ov,  ovules  ;  pi,  placenta  ; 
tu,  tube  of  the  perianth 
inclosing  the  style  ;  sta, 
stamen  ;  sti,  stigma  :  o, 
ovary.     (After  Gray.) 


Fig.  2  9  2  .  — Vertical 
section  of  iris  flower,  with 
perianth  removed,  showing 
a  stamen  and  three  stig- 
mas: «/,  stigmatic  surface. 


Fig.  293.  — Cross  sec- 
tion of  ovary  of  iris  flower  : 
c,  c,  carpels ;  /,  /,  locules ; 
Oil,  ovules ;  pi,  placenta. 


206         PRACTICAL  COURSE  IN  BOTANY 

Remove  the  perianth  and  sketch  the  remaining  organs  in 
profile,  showing  the  position  of  the  stamens.  Do  you  see 
any  advantage  in  their  position?  Can  you  determine  the 
use  of  the  crest  of  hairUke  filaments  on  the  upper  side  of  the 
sepals  ?     Remove  a  stamen  and  sketch  it. 

223.  The  pistil.  —  Remove  as  much  of  the  upper  part  of 
the  perianth  tube  as  you  can  without  injuring  the  pistil, 
and  with  a  sharp  knife  cut  a  vertical  section  down  through 
the  ovary  so  as  to  show  the  long  style  and  its  connection  with 
the  placenta.  Make  a  sketch  of  this  longitudinal  section 
(see  Fig.  291),  labeling  the  parts  observed.  Notice  whether 
the  placenta  is  central  or  parietal.  Draw  a  cross  section  of 
the  ovary ;  how  many  locules  has  it  ?  How  many  ovules  in 
each?  Where  are  they  attached?  Is  the  placenta  free 
central  or  axial  (Fig.  293)  ?  Examine  with  a  lens  the  little 
flap  at  the  base  of  the  two-cleft  apex  of  one  of  the  stigmas,  and 
look  for  a  moist  spot  to  which  the  pollen  will  adhere.  Label 
this  in  your  sketch,  stigmatic  surface.  No  seeds  can  be  ma- 
tured unless  some  of  the  pollen  reaches  this  surface  ;  can  you 
think  by  what  agency  it  is  carried  there?  What  insects 
have  you  seen  hovering  about  the  iris?  Notice  that  in 
drawing  his  head  out  of  the  flower,  an  insect  would  not 
touch  the  stigmatic  surface,  since  it  is  on  the  upper  side  of 
the  flap  and  he  would  be  probing  under  it.  But  in  entering 
the  next  flower  that  he  visits,  he  is  likely  to 
strike  his  head  against  the  flap  and  turn  it 
under,  thus  dusting  it  with  pollen  brought 
from  another  flower. 

224.  Diagrams.  —  Draw  diagrams  show- 
ing the  horizontal  and  vertical  arrangement 
Fir..  294  —  Tiori-  of  parts  iu  the  iris  or  other  specimen  ex- 
flower.'^'^^'''"""^^''  amined,  and  compare  with  those  made  of 
the  monocotyl  studied  in  the  preceding  sec- 
tion. In  what  respect  does  it  differ  from  them?  How  do 
you  account  for  the  difference  in  the  number  of  stamens,  if 
there  is  any?     (220.) 


THE   FLOWER 


207 


225.  The  vertical  order,  —  The  difference  in  vertical 
arrangement  is  an  important  one.  Bear  in  mind  that  flowers 
of  this  type  have  the  ovary  inferior,  that  is,  inserted  under 
the  other  organs  (Figs.  296,  304),  which  are  then  said  to  be 
superior,  or  epigynous,  a  word  which,  as  you  know  from  the 
prefix  epi  (47),  means  over  or  above  the  pistil.  To  make  the 
matter  clear,  the  two  sets  of  terms  employed  for  describing 
the  position  of  the  ovary  are  given  below  in  parallel  columns: 


Hypogynous 

Ovary  superior 

Calyx  or  perianth  inferior 


Epigynous 

Ovary  inferior 

Calyx  or  perianth  superior 


The  epigynous  arrangement  is  considered  as  marking  a 
higher  stage  of  floral  development   than   the  hypogynous, 
which  is  characteristic  of  a  more 
simple  and  primitive  structure. 

226.  Dissection   of   a   dicotyl 
flower.  —  Sketch   a   blossom   of 
quince  or  apple,  fuchsia,  evening 
primrose,  etc.,  first  from  the  out- 
side, then  from  the  inside,  and 
then  in  vertical  section,  labeling 
the  parts  as  in 
your     other 
sketches.    No- 
tice in  the  pear 
or   apple  how 
the    ovary    is 
sunk     in     the 
hollowed-out 
receptacle. 
Where  are  the 
other      parts 

attached  ?  Are  they  inferior  or  superior  ?  Hold  up  a  petal 
to  the  light  and  examine  its  venation  through  a  lens.  (Use 
for  this  purpose  a  petal  from  a  flower  that  has  stood  in  red 
ink  for  two  or  three  hours.)     Is  it  parallel-veined  or  net- 


Fius.  295-296.  —  Evening  primrose,  dicotyl  flower  with  in- 
ferior ovary  :  295,  exterior  view ;  296,  longitudinal  section, 
showing  vertical  arrangement  of  parts. 


208 


PRACTICAL  COURSE  IN  BOTANY 


veined?     If  the  flowers  are  clustered,  what  is  the  order  of 
inflorescence?     Does   the  position  of  the   flowers  on  their 

branch  correspond  to  that  of 

297  298  1         1       c  -1 

the  leaf  axils  on  the  same 
kind  of  plant  ? 

227.  The  stamens,  —  Re- 
move the  petals  from  a  flower 
and  examine  the  stamens 
with  a  lens.  Notice  the  at- 
tachment and  shape  of  the 
anthers.  Are  they  all  of  the 
same  color?  How  do  you 
account  for  the  difference,  if 
there  is  any?  Is  the  posi- 
tion of  the  pistil  and  stamens 
such  that  the  pollen  from 
the  anthers  can  readily  reach 
the  stigmas  without  external 
aid?  Examine  the  pistil  in 
flowers  of  different  ages,  and 
see  if  the  stigma  is  mature  (that  is,  moist  and  sticky)  at  the 
same  time  that  the  anthers  are  discharging  their  pollen. 
Make  an  enlarged  sketch  of  a  stamen  showing  the  shape  of 
the  anther  and  the  method  of  opening  to  discharge  pollen. 
228.  The  pistils.  —  How  many  pistils  do  you  find  in  the 
apple  blossom  (or  other  flower  under  examination)  ?  Are  they 
distinct,  or  united  ?  Find  where  the  styles  originate ;  what 
do  you  see  there  ?  Make  a  cross  section  of  the  ovary  and 
count  the  locules;  how  does  their  number  compare  with 
that  of  the  styles  ?  Can  you  make  out  the  number  of  ovules 
in  each  ?  If  not,  use  a  young  fruit ;  as  it  is  only  an  enlarged 
ovary,  it  will  show  the  parts  correctly.  Compare  it  with  a 
ripe  fruit  and  see  if  all  the  ovules  matured.  Can  you  think 
of  any  reasons  why  some  of  them  might  fail?  Do  you  see 
any  signs  of  nourishment  stored  in  the  ovary?  Name  all 
the  ways  you  can  think  of  in  which  the  ovary  can  benefit  the 


299  300 

Figs.  297-300.  —  Flower  and  sections 
of  pear  :  297,  cluster  of  blossoms,  showing 
inflorescence;  298,  vertical  section  of  a 
flower ;  299,  ground  plan  of  a  flower ;  300, 
vertical  section  of  fruit. 


THE  FLOWER 


209 


ovules  and  seeds.     Draw  the  ovary  in  cross  and  vertical 
sections,  labeling  correctly  all  the  parts. 

229.  The  numerical  plan  of  dicotyls.  —  Diagram  the  plan 
of  the  flower  in  cross  and  vertical  section.  How  many  parts 
are  there  in  each  set  ?  Can  you  tell  readily 
the  number  of  stamens  ?  When  the  indi- 
viduals of  any  set  or  cycle  of  organs  are  too 
numerous  to  be  easily  counted,  like  the 
stamens  of  the  apple,  pear,  and  peach,  or 
the  petals  of  the  water  lily,  they  are  said 
to  be  indefinite.  It  is  very  seldom  that  per- 
fect symmetry  is  found  in  all  parts  of  the 
flower.  The  stamens  and  pistil,  in  partic- 
ular, show  a  great  tendency  to  variation,  so 
that  the  numerical  plan  is  generally  deter- 
mined by  the  calyx  and  corolla.  Where  the 
parts  are  in  fives,  as  in  the  pear,  quince,  and  wild  rose,  the 
flower  is  said  to  be  pentamerous,  or  in  sets  of  five.  This  is  the 
prevailing  number  among  dicotyls,  though  other  orders  are 


Fig.  301.  — VertP 
cal  section  of  an  al* 
mond  blossom  with 
petals  removed,  show- 
ing the  perigynoua 
arrangement. 


302 


W.i 


304 


Figs.  302-304.  —  Diagrams  showing  arrangement  of  parts  with  reference  to  the 
ovary:  bd,  receptacle;  A-,  calyx ;  A:/-,  corolla;  st,  stamens;  fr,  ovary;  g,  style;  n, 
stigma ;  302,  perigynous ;  303,  hypogynous ;  304,  epigynous. 

not  uncommon.  In  the  mustard  family  (220)  and  other 
well-known  species,  the  fourfold  order  prevails,  while  some 
of  the  saxifrages  have  their  parts  in  twos,  and  the  magnolia 
and  the  pawpaw  have  a  threefold  arrangement. 


210 


PRACTICAL  COURSE  IN  BOTANY 


230.  Intermediate  types.  —  Flowers  like  the  peach  and 
rose  represent  an  intermediate  type  in  which  the  calyx, 
petals,  and  stamens  are  attached  to  a  prolongation  of  the 
receptacle  that  extends  above  the  ovary,  but  is  not  united 
with  it  (Fig.  301 ).  in  general,  a  flower  is  not  considered  as 
belonging  to  the  epigynous  kind  unless  the  ovary  is  more  or 
less  consolidated  with  the  parts  around  it  (Fig.  304). 


III.    STUDY    OF    A    COMPOSITE    FLOWER 

Material.  —  The  largest  lieads  attainable  should  be  selected,  as  the 
florets  are  small  at  best,  and  difficult  to  handle.  The  large  cultivated  sun- 
flower {Helianthus  annuus)  makes  an  ideal  specimen,  if  accessible.  Oxeye 
daisy  and  dandelion  can  be  obtained  throughout  the  season  almost  every- 
where, but  the  former  has  no  pappus,  and  the  latter  does  not  show  the 
tubular  disk  flowers.  Other  common  sjiecimens  an; :  for  spring,  mayweed, 
Jerusalem  artichoke,  coreopsis,  arnica;  for  late  summer  and  autumn, 
China  aster,  golden  aster  (Chrysopsis),  sneezeweed,  elecampane  —  and, 
in  fact,  the  great  majority  of  flowers  to  be  found  at  this  season  are  of  the 
composite  family.  Oxeye  daisy  is  used  as  a  model  in  the  text  on  account 
of  its  general  accessibility,  but  almost  any  specimen  of  the  radiate  kind 
will  meet  all  essential  conditions  of  the  analysis. 

231.  The  ray  flowers. 

eye  daisy  through  a  lens. 


-  Examine  the  upper  side  of  an  ox- 
Of  what  is  the  yellow  button  in  the 


center  composed?     Count  the  narrow, 


petal-like  rays  dis- 
posed around 
the  center.  To 
decide  what  they 
are,  look  for  a 
small  two-cleft 
body  at  the  base 
of  the  ray;  this 
is  the  pistil. 
Do  you  see  any 
stamens    in   the 


305 


307 

Figs.  305-308.  —  An  oxeye  daisy  :  305,  a  flower  head  ; 
306,  vortical  section  of  a  head ;  307,  disk  flower ;  308,  ray 
flower,  enlarged. 


ray 


An  exam- 


ination will  show 
that  all  the  rays 


THE   FLOWER  211 

contain  pistils,  but  no  stamens ;  they  are,  therefore,  not  petals, 
but  the  corollas  of  imperfect  flowers.  Look  at  the  upper  edge 
of  a  ray  of  sneezeweed,  coreopsis,  arnica,  chicory,  etc.,  for 
small  teeth  or  notches  ;  these  represent  the  lobes  of  a  sympet- 
alous corolla.  Split  one  of  the  tubular  corollas  of  the  disk 
down  one  side  and  open  it  out  flat ;  does  it  throw  any  light 
on  the  morphology  of  the  ray  ?  In  many  composite  plants, 
as  the  sunflower,  coneflower,  coreopsis,  the  rays  are  all  neutral; 
that  is,  they  have  neither  pistil  nor  stamens.  Are  they  of  any 
use  in  such  cases  ?  If  you  are  in  doubt,  remove  all  the  rays 
from  a  head ;  would  the  disk  be  noticeable  enough  to  attract 
attention  without  them?  What  is  the  principal  office  of 
the  rays? 

232.  The  involucre.  —  Look  at  the  cluster  of  green,  leafy 
scales  on  the  under  side  of  the  head.  It  is  not  a  calyx,  but 
a  collection  of  bracts,  called  an  involucre.  Have  you  ever 
noticed  the  bracts  under  the  separate  flowers  on  a  raceme? 
(16L)  What  would  be  the  position  of  the  bracts  if  all  the 
flowers  of  the  raceme  were  compacted  into  a  head  like  the 
daisy  or  sunflower?  Is  the  involucre  of  any  use?  Cut  it 
away  gently  so  as  not  to  disturb  the  other  organs  and  see 
what  happens  to  the  rays. 

233.  The  disk  flowers.  —  Cut  a  vertical  section  through 
the  head  of  a  flower  and  notice  the  broad,  flat  receptacle  (in 
some  cases  round  or  columnar)  on  which  the  tinj^  florets 
are  seated.  Observe  whether  it  is  naked,  or  whether  it 
bears  chaffy  scales  inclosing  the  florets.  Make  an  enlarged 
drawing  of  this  section,  showing  the  insertion  of  the  dif- 
ferent parts  and  labeling  them  all  correctly.  What  differ- 
ences do  you  observe  between  the  disk  and  the  ray  flowers  ? 

234.  The  pappus.  — ^  Open  one  of  the  disk  flowers  with  a 
dissecting  needle  and  observe  the  small  striate  (in  some 
specimens,  hairy)  body  to  which  the  base  of  the  style  is  at- 
tached. This  is  the  ovary,  inclosed  in  the  lower  part  of  the 
calyx,  which  has  become  incorporated  with  it.  "When  mature, 
it  will  form  a  small,  one-seeded  fruit  called  an  akene.     Can 


212 


PRACTICAL  COURSE  IN  BOTANY 


you  see  the  ovule?  Where  is  it  attached?  (Use  a  mature 
akene  for  this  purpose.)  In  most  plants  of  this  family,  the 
akene  is  surmounted  by  delicate  hairy  bristles,  as  in  the 
dandelion,  wild  lettuce,  and  groundsel ;  or  by  small  chaffy 
scales,  as  in  the  sneezeweed  and  sunflower,  and  sometimes 
by  hooks  and  barbed  hairs,  like  those  of  the  tickseed,  bur 
marigold,  and  cocklebur.  These  appendages  constitute  the 
pappus.  They  are  modifications 
of  the  sepals,  and  serve  an  impor- 
tant purpose  in  aiding  the  dis- 
tribution of  the  seed.      Can  you 


312 


313 


314 


Figs.  309-314.  —  Akenes  of  the  composite  family:  309,  mayweed  (no 
pappus);  310,  cliicory  (pappus  a  shallow  cup);  311,  sunflower  (pappus  of  two 
deciduous  scales) ;  312,  sneezeweed  (.Helenium,  pappus  of  five  scales) ;  313,  sow 
thistle  (pappus  of  delicate  downy  hairs)  ;  314,  dandelion,  tapering  below  the 
pappus  into  a  long  beak.     (After  Gray.) 


suggest  some  of  the  ways  in  which  they  may  aid  in  accom- 
plishing this  object? 

235.  The  stamens  and  pistil.  —  Remove  the  corolla  of  a 
disk  flower  carefully  so  as  not  to  disturb  the  inclosed  organs, 
and  notice  how  the  stamens  are  united  into  a  tube  by  their 
anthers.  Flatten  out  the  tube  and  make  an  enlarged  sketch 
of  it,  showing  the  long,  narrow  shape  of  the  anthers  and  their 
mode  of  attachment.  Can  you  make  out  how  they  open  to 
discharge  their  pollen  ?  Examine  one  of  the  younger  florets 
near  the  center  of  the  disk,  and  observe  that  the  tip  of  the 
style  is  inclosed  in  the  anther  tube  with  the  lobes  of  the 
stigma  pressed  tightly  together  by  their  inner  faces  (Fig.  315), 
so  that  it  is  impossible  for  any  of  the  pollen  to  reach  the  stig- 


THE   FLOWER 


213 


316 


317 


matic  surface.  It  remains  in  this  position  till  the  anthers  have 
shed  their  pollen,  then,  as  may  be  seen  by  examining  an  older 
flower,  the  style  begins  to  elongate,  pushing  up  the  pollen 
that  has  fallen  on  the  hairy  outside  of  the  closed  stigma,  and 
forcing  it  out  of  the  corolla  tube,  where  it  can  be  scattered 
by  insects  among  the  other 
flowers  of  the  cluster.  When 
the  pollen  of  its  own  floret 
has  been  thus  disposed  of,  the 
stigma  lobes  open  and  curl 
outward,  ready  to  receive  the 
pollen  from  other  flowers. 
This  arrangement  is  practi- 
cally universal  among  plants 
of  the  composite  family ;  can 
you  divine  its  object?  It 
will  be  shown  later,  that  much 
larger  and  stronger  seeds  are 
produced  when  the  pistil  is 
pollinated  from  a  different 
flower,  or,  better  still,  from  a 
different  plant  of  the  same 
species  ;  hence,  you  see  what 
a  useful  adaptation  this  is. 

236.  Nature  of  a  composite  flower.  —  It  will  be  evident, 
from  the  examination  just  made,  that  the  daisy,  dandelion, 
sunflower,  etc.,  are  not  single  flowers,  but  compact  heads 
of  small  blossoms  so  closely  united  as  to  appear  like  a  single 
individual ;  hence  they  are  said  to  be  composite,  or  com- 
pound. They  are  the  most  numerous  and  widely  dissem- 
inated of  all  plants,  comprising  one  seventh  of  the  entire 
flowering  vegetation  of  the  globe,  and  are  regarded  by 
botanists  as  representing  the  most  advanced  stage  of  floral 
evolution.  Can  you  point  out  some  of  the  adaptations  to 
which  their  success  in  solving  the  problems  of  plant  life  is 
due?     (164.) 


315 

Figs.  315-317.  —  Flowers  of  Arnica 
montajm,  showing  successive  stages  in  pol- 
lination :  315,  pistil  just  extruding  from 
anther  tube,  covered  with  pollen,  but  with 
stigmatic  surfaces  closed;  316,  stigma 
opened  and  mature  ;  317,  stigma  recurved 
to  receive  pollen  from  its  own  or  neigh- 
boring anthers  if  foreign  pollen  has  not 
reached  it. 


214  PRACTICAL  COURSE   IN  BOTANY 


IV.     SPECIALIZED   FLOWERS 

Material.  —  For  spring  and  early  summer:  sweet  pea,  black  locust, 
wistaria,  lui)ine,  or  any  of  the  characteristic  butterfiy-shaped  Huwers  of 
the  pea  family.  For  autmnn  or  late  smnmer :  tropa?olmn,  monkshood, 
or  a  bilabiate  flower  —  snapdragon,  digitalis,  dead  nettle,  salvia,  catalpa, 
etc.  —  of  the  mint  or  figwort  family. 

237.  Irregularity   and    specialization.  —  Irregularity   and 

bilateral  regularity  are,  as  a  rule,  indicative  of  specialization, 
or  adaptation  to  a  particular  purpose,  such  as  the  ready 
distribution  of  pollen,  or  its  protection  against  injury.  These 
adaptations  are  more  noticeable  in  the  corolla  than  in  other 
parts,  and  hence  flowers  of  this  kind  are  usually  classed 
according  to  the  shape  of  their  corollas.  The  most  highly 
specialized  flowers  in  this  respect  are  the  orchids,  but  they 
are  too  rare  and  difficult  of  access  to  be  available  objects  for 
study.  The  most  familiar  and  widely  distributed  kinds  of 
speciahzed  corollas  are  the  bilabiate,  or  two-lipped,  and  the 
papilionaceous,  or  butterfly,  forms.  The  first  is  characteris- 
tic of  the  mint  and  figwort  families,  of  which  the  toadflax, 
sage,  and  catalpa  are  familiar  examples.  The  second  com- 
prises the  well-known  papilionaceous  flowers  of  the  pea 
family,  named  from  the  Latin  word  papilio,  a  butterfly,  on 
account  of  their  general  resemblance  to  that  insect. 

238.  Dissection  of  a  papilionaceous  flower.  —  Sketch  a 
blossom  of  any  kind  of  pea  or  vetch  as  it  appears  on  the 
outside.  Are  the  sepals  all  of  the  same  length  and 
shape?  If  not,  which  are  the  shorter,  the  upper  or  the 
lower  ones? 

Turn  the  flower  over  and  examine  its  inner  face.  Notice 
the  large,  round,  and  usually  upright  petal  at  the  back,  the 
two  smaller  ones  on  each  side,  and  the  boat-shaped  body 
between  them,  formed  of  two  small  petals  more  or  less  united 
at  the  apex.  Press  the  side  petals  gently  down  with  the 
thumb  and  forefinger  and  notice  how  the  essential  organs  are 
forced  out  from  the  little  boat  in  which  they  are  concealed. 


THE  FLOWER 


215 


Observe  how  the  end  of  the  style  is  bent  over  so  as  to  bring 
the  stigma  uppermost  when  the  petals  are  depressed.  Imag- 
ine the  legs  of  a  bee  or  a  butterfly  resting  there  as  he  probed 
for  honey ;  with  what  organ  would  his  body  first  come  in 
contact  when  he  alighted?  If  his  thorax  and  abdomen  had 
previously  become  dusted  with  pollen  when  visiting  another 
flower,  where  would  the  pollen  be  deposited  ?  Do  you  notice 
anything  in  the  color,  shape,  or  odor  of  this  flower  that  would 
be  likely  to  attract  insects  ?     Have  you  ever  observed  insects 


Figs.  318-322.  —  Dissection  of  a  papilionaceous  flower:  318,  front  view  of  a 
corolla;  319,  the  petals  displayed:  «,  vexillum,  or  standard;  w,  wings;  A;,  keel ; 
320,  side  view  with  all  except  one  of  the  lower  petals  removed,  showing  the  essential 
organs  protected  in  the  keel :  I,  loose  stamen  ;  st,  stamen  tube  ;  321,  side  view, 
showing  how  the  anthers  protrude  when  the  keel  is  depressed  ;  322,  ground  plan. 
{After  Gray.) 

hovering  around  flowers  of  this  kind ;  for  example,  in  clover 
and  pea  fields,  and  about  locust  trees  and  wistaria  vines? 
What  kind  of  insects,  chiefly,  have  you  seen  about  them  ? 

Remove  the  sepals  and  petals  from  one  side,  and  sketch 
the  flower  in  longitudinal  section,  showing  the  position  of  the 
pistil  and  stamens.  Then  remove  all  the  petals,  and  spread 
in  their  natural  order  on  the  table  before  you,  and  sketch  as 
they  lie  (Fig.  319).  Label  the  large,  round  upper  one, 
standard  or  vexiUum;  the  smaller  pair  on  each  side,  wings, 
and  the  two  more  or  less  coherent  ones  in  which  the  pistil 
and  stamens  are  contained,  keel. 

239.  The  stamens.  —  Count  the  stamens,  and  notice 
how  they  are  united  into  two  sets  of  nine  and  one.     Stamens 


21G  PRACTICAL  COURSE   IN   BOTANY 

united  in  this  way,  no  matter  what  the  number  in  each  set, 
are  said  to  be  diadelphous,  that  is,  in  two  brotherhoods. 
Notice  the  position  of  the  lone  brother,  whether  below  the 
pistil  —  next  to  the  keel  —  or  above,  facing  the  vexillum. 
Would  the  projection  of  the  pistil,  when  the  wings  are  de- 
pressed, be  facilitated  to  the  same  extent  if  the  opening  in  the 
stamen  tube  were  on  the  other  side,  or  if  the  filaments  were 
monadelphous  —  all  united  into  one  set  ?  Flatten  out  the 
stamen  tube,  or  sheath,  formed  by  the  united  filaments,  and 
sketch  it. 

240.  The  pistil.  —  Remove  all  the  parts  from  around  the 
pistil,  and  sketch  it  as  it  stands  upon  the  receptacle.  Look 
through  your  lens  for  the  stigmatic  surface  (223).  See  if 
there  are  any  hairs  on  the  style,  and  if  so,  whether  they 
are  on  the  front,  the  back,  or  all  around.  Can  you  think  of  a 
use  for  these  hairs?  Notice  how  the  long,  narrow  ovary  is 
attached  to  the  receptacle ;  is  it  sessile,  or  raised  on  a  short 
footstalk?  If  the  latter,  label  the  footstalk,  stijje.  Select  a 
well-developed  pistil  from  one  of  the  lower  flowers,  open  the 
ovary  parallel  with  its  flattened  sides,  and  sketch  the  two 
halves  as  they  appear  under  the  lens.  Notice  to  which  side 
the  ovules  are  attached,  the  upper  (toward  the  vexillum)  or 
the  lower,  and  label  it,  placenta.  How  many  locules  has  the 
ovary?     How  many  carpels?     How  can  you  tell  (216)  ? 

241.  Plan  of  the  flower.  —  Diagram  the  flower  in  hori- 
zontal and  vertical  section,  and  decide  upon  the  following 
points :  — 

Numerical  plan 
Symmetry 
Regularity 
Union  of  i)arts 
Position  of  tlio  ovary 

242.  Significance  of  these  distinctions.  —  These  distinc- 
tions are  important  to  remember,  not  only  because  they  are 
very  useful  in  grouping  and  classifying  plants,  but  because 
they  mark  successive  stages  in  the  evolution  of  the  flower. 
In  general,  flowers  of   a  primitive  type  and  less  advanced 


THE   FLOWER 


217 


organization  are  characterized  by  having  their  organs  free 
and  hypogynous,  while  the  more  highly  developed  forms  show 
a  tendency  to  consolidation  and  union  of  parts,  and  the 
epigynous  mode  of 
insertion.  Irregular- 
ity also,  since  it  in- 
dicates specialization 
and  adaptation  to  a 
particular  purpose, 
may  be  regarded  as  a 
mark  of  advanced 
evolution. 

243.  Dissection  of 
a  bilabiate  flower. — 
Make  a  similar  study 
of  the  flower  of  a 
salvia,  dead  nettle, 
catalpa,  or  other  spec- 
imen of  the  bilabiate 
kind.  Make  diagrams 
and  report  as  to  (1)  numerical  plan ;  (2)  presence  or  absence 
of  parts  ;  (3)  regularity  ;  (4)  union  of  parts  ;  (5)  position  of 
ovary.     Observe  especially  the  relative  position  of  stigma 


Figs.  323,  324.  — Salvia:  323,  a  newly  opened 
flower,  showing  the  pollen-covered  anther  striking 
the  back  of  a  visiting  bee ;  324,  an  older  flower, 
witli  the  protruding  pistil  rubbing  against  the  back 
of  a  bee  covered  with  pollen  from  a  younger  flower. 


325  'd 

Figs.  325,  326.  —  Salvia :  325,  longitudinal  section  through  a  flower,  showing 
the  rocking  connective  which  is  struck  at  o  by  a  visiting  insect ;  326,  section  of  the 
same  flower  after  being  visited,  showing  the  lower  arm  of  the  connective  pushed 
back  and  lowering  the  anther. 

and  anthers ;  is  it  such  that  the  pollen  can  reach  the  stigma 
without  external  aid  ?  Does  the  peculiar  shape  of  the  corolla 
serve  any  other  purpose  than  to  attract  the  attention  of 


218 


PRACTICAL  COURSE  IN  BOTANY 


insect  visitors  by  its  conspicuous  appearance  ?  What  is  the 
use  of  the  projecting  underlip?  Is  it  any  convenience  to  a 
bee,  for  instance,  to  have  a  platform  to  rest  on  while  gather- 
ing pollen  or  honey?  What  is  the  use  of  the  arched  upper 
hp  ?  Cut  it  away  and  notice  the  exposed  condition  of  the 
stamens  and  pistil.  Turn  a  flower  upside  down;  what 
would  be  the  effect  on  a  visiting  bee  or  butterfly?  (Exps. 
83,  84.) 

244.  Morphology  of  the  flower.  —  We  have  seen  that  the 
venation  of  petals  and  sepals  corresponds  in  a  general  way 
with  that  of  foliage  leaves  of  the  class  to 
which  they  belong,  and  that  their  arrange- 
ment around  their  axis  is  analogous  to  the 
arrangement  of  foliage  leaves  on  the  branch. 

In  our   study  of 

inflorescence,      it 

was  observed  that 

flowers  and  flower 

buds  occur  in  the 

same       positions 

where    leaf    buds 

occur,    and    that 

they  are  subject 

to  the  same  laws 

of      arrangement 

and  growth.  We 
learned,  also,  in  our  study  of  leaves,  some- 
thing about  the  wonderful  modifications  that 
these  organs  are  capable  of  undergoing ;  and 
finally,  an  examination  of  a  number  of  different  flowers  has 
shown  them  capable  of  undergoing  modifications  to  an  equal 
or  even  greater  extent,  and  examples  of  the  transition  of 
almost  any  floral  organ  into  another  may  be  observed  by  one 
who  will  take  the  trouble  to  look  for  it.  Stamens  and  petals 
are  found  in  all  stages  of  transformation,  from  the  slightly 
flattened  filament  of   the  star-of-Bethlehem,  or  the  yellow 


Fig.  327.  —  Staminodia,  trans- 
formed stamens  of  canna  simu- 
lating petals :  pet,  petals ;  st 
staminodia. 


Fig.  328.— 
Flower  of  a  cactus 
{cereus  grcggiOi 
showing  transitior 
from  scales  to 
petals. 


THE  FLOWER  219 

pollen  speck  on  the  petal  of  a  rose,  to  the  brilliant  staminodia, 
or  transformed  stamens  of  the  canna  (Fig.  327),  which  simu- 
late petals  so  perfectly  that  their  real  nature  is  never  sus- 
pected by  the  ordinary  observer.  The  transition  from  spines 
and  bracts  to  the  brilliant  corolla  of  the  cactus  (Fig.  328) 
is  so  gradual  that  we  are  hardly  aware  of  it  till  we  examine  a 
specimen  and  see  it  actually  going  on  before  our  eyes. 

It  must  not  be  supposed,  however,  that  an  organ  is  ever 
developed  as  one  thing  and  then  deliberately  changed  into 
something  else.  When  we  speak  loosely  of  one  organ  being 
modified  into  another,  the  meaning  is  merely  that  it  has  de- 
veloped into  one  thing  instead  of  into  something  else  that  it 
was  equally  capable  of  developing  into. 

245.  The  course  of  floral  evolution.  —  For  the  reasons 
mentioned,  the  flower  is  regarded  as  merely  a  branch  with 
modified  leaves  and  the  internodes  indefinitely  shortened  so 
as  to  bring  the  successive  cycles  into  close  contact,  the  whole 
being  greatly  altered  and  specialized  to  serve  a  particular 
purpose.  With  this  conception  of  the  nature  of  the  flower, 
we  can  readily  see  that  the  less  specialized  its  organs  are  and 
the  more  nearly  they  approach  in  structure  and  arrangement 
to  the  condition  of  an  undifferentiated  branch,  the  more 
primitive  and  undeveloped  is  the  type  to  which  it  belongs. 
On  the  other  hand,  if  the  parts  are  highly  specialized  and 
widely  differentiated  from  the  crude  branch,  a  proportion- 
ately high  stage  of  floral  evolution  is  indicated. 

V.     FUNCTION    AND    WORK    OF    THE    FLOWER 

Material.  —  For  this  exercise,  flowers  of  the  mallow  family  —  holly- 
hock, abutilon,  mallow,  hibiscus,  cotton,  okra,  etc.  —  are  particularly 
recommended  because  they  have  pollen  grains  so  large  that  they  can  be 
studied  fairly  well  with  a  hand  lens.  Lily,  tulip,  iris,  etc.,  will  also  meet  all 
essential  conditions  of  the  study  outlined  in  the  text.  A  strand  of  silk 
from  a  pollinated  ear  of  corn  is  an  excellent  example  for  showing  the 
growth  of  the  pollen  tube,  under  the  microscope. 

Appliances.  —  A  compound  microscope ;  a  watch  crystal ;  sugar  solu- 
tion of  5  to  15  per  cent. 


220  PRACTICAL  COURSE   IN   BOTANY 

Experiment  77.  To  show  the  germination  of  pollen  grains.  — 
Put  a  drop  of  5  per  cent  sugar  solution  into  a  watch  crystal  or  a  concave 
slide,  seal  by  smearing  the  edges  witli  vaseline,  and  cover  with  a  glass 
to  keep  out  the  dust.  Examine  at  intervals  of  five  minutes  under  the 
microscope  (a  hand  lens  will  sho\v  the  result  with  the  specimens  recom- 
mended, though  not  so  well),  and  ihe  pollen  grains  will  be  observed  to  send 
out  long  filaments  or  tubes  into  the  sirup,  as  a  germinating  seedhng  sends 
its  radicle  into  the  soil. 

246.  Office  of  the  flower.  —  The  one  object  of  the  flower 
is  the  production  of  fruit  and  seed,  and  all  its  wonderful 
specializations  and  variations  of  form  and  color  tend  either 
directly  or  indirectly  to  this  end. 

247.  Pollination  and  fertilization.  —  It  was  stated  in  215 
that  only  in  very  exceptional  cases  can  seed  be  developed 
unless  some  of  the  pollen  reaches  the  stigma.  This  act, 
called  polliriation,  is  an  essential  step  in  seed  production,  but 
is  not  sufficient  to  secure  that  end  unless  it  leads  to  the  process 
known  as  fertilization.  Successful  pollination  is  a  necessary 
preliminary  to  fertilization,  and  the  one  begins  where  the 
other  ends. 

248.  The  next  step  toward  fertilization.  —  Examine  with  a 
lens  the  pollinated  pistil  of  a  mallow,  lily,  or  other  large 
flower,  and  notice  the  flabby,  withered  appearance  of  grains 
that  have  stood  for  some  time  on  the  stigma,  as  com- 
pared with  those  of  a  newly  opened  anther.  Can  you  ac- 
count for  the  difference?  Touch  the  tip  of  your  tongue 
to  the  stigma,  or  apply  the  proper  chemical  test,  and  it  will 
be  seen  that  the  sticky  fluid  which  it  exudes,  contains  sugar. 
Refer  to  Exp.  77  and  say  what  effect  this  substance  has 
on  the  pollen. 

249.  The  pollen  tube.  —  The  same  thing  happens  when  a 
pollen  grain  falls  on  the  moist  surface  of  the  stigma.  It 
begins  to  germinate  by  sending  a  little  tube  down  into  the 
substance  of  the  pistil,  and  the  withered  appearance  of  the 
grains  on  the  stigma  results  from  the  nourishment  in  them 
having  been  exhausted,  just  as  the  endosperm  of  the  seed  is 
exhausted  when  the  embryo  begins  to  germinate.   Here,  how- 


THE  FLOWER  221 

ever,  the  analogy  ends,  for  the  pollen  tube  is  not  adapted,  like 

the  radicle  of  the  seedling,  to  absorb  and  convey  nourishment 

up  to  the  other  parts,  but  to  feed  and  carry  down  to  the  ovary 

two    small  bodies    called    generative    cells, 

which  it  discharges  there,  and  then  its  work 

is  done  and  it  disappears.     So  it  must  be 

borne  in  mind  that  when  we  speak  of  the 

germination  of  the  pollen  grains,  we  mean 

something  really  very  different  from  the 

germination  of  a  seed. 

250.  The  course  of  the  pollen  tube.  — 
Cut  the  thinnest  possible  section  through 
a  freshly  pollinated  pistil  and  place  under 
the  microscope.  Watch  the  pollen  tubes 
from  the  grains  on  the  stigma  as  they  de- 
scend through  the  style  toward  the  ovary.  poiferg;ain'emittint 
A  pollinated  strand  of  corn  silk  —  which  is  a  tube  (magnified). 
only  a  very  much  elongated  style  —  is  excellent  for  this  pur- 
pose. It  is  so  thin  and  transparent  that  no  section  need  be 
made,  and  the  tube  can  be  traced  as  it  works  its  way  down 
through  the  entire  length  of  the  threadlike  style  to  the  young 
grain,  or  ovary,  on  the  cob.  The  time  required  for  the  tube 
to  penetrate  to  the  ovary  varies  in  different  flowers  according 
to  the  distance  traversed  and  the  rate  of  growth.  In  the 
crocus  it  takes  from  one  to  three  days ;  in  the  spotted  calla, 
about  five  days ;  and  in  orchids,  from  ten  to  thirty  days. 
As  a  rule,  it  occupies  only  a  few  hours.  Sometimes  the  pis- 
til is  hollow,  affording  a  free  passage  to  the  pollen  tube; 
in  other  cases,  it  is  solid,  and  the  growing  tube  eats  its  way 
down,  as  it  were,  feeding  on  the  substance  of  the  pistil 
as  it  grows.  How  is  it  in  the  flower  you  are  examining  ?  It 
takes  a  grain  of  pollen  to  fertilize  each  ovule,  and  where  more 
than  one  seed  is  produced  to  a  carpel,  as  is  commonly  the 
case,  at  least  as  many  pollen  tubes  must  find  their  way  to 
each  locule  of  the  ovary  as  there  are  ovules  —  provided  all 
are  fertilized. 


222 


PRACTICAL  COURSE  IN  BOTANY 


251.  Fertilization.  —  When  a  pollen  tube  has  penetrated 
to  the  ovary,  it  next  enters  one  of  the  ovules,  usually  through 

the  micropyle  (Fig.  330,  m). 
There  it  penetrates  the  wall  of 
a  baglike  inclosure  called  the 
embryo  sac  (Fig.  330,  u,  t,  z), 
where  one  of  the  generative 
cells  emitted  by  the  pollen  tube 
fuses  with  a  large  cell  contained 
in  the  embryo  sac,  known  as 
the  germ  cell,  or  egg  cell  (Fig. 
330,  z).  The  fusion  of  these 
two  bodies  is  what  constitutes 
fertilization.  The  cell  formed 
by  their  union  finally  develops 
into  the  embryo,  and  the  other 
contents  of  the  sac  into  the 
endosperm,  and  the  ripened 
ovules  become  seeds. 

252.  Stability  of  the  process 
of  fertilization.  —  The  phe- 
nomena that  characterize  the 
functions  of  fertilization  and 
reproduction  are  the  most  uni- 
form and  stable  of  all  the  life 
processes,    varying    little    not 


Fig.  330.  —  Diagram  of  a  simple 
flower,  showing  course  of  the  pollen 
tube :  a,  trans  verse  section  of  an 
anther  before  its  dehiscence;  6,  an 
anther  dehiscing  longitudinally,  with 
pollen ;  c,  filament ;  d,  base  of  floral 
leaves ;  e,  nectaries  ;  /,  wall  of  carpels ; 
g,  style ;  h,  stigma ;  i,  germinating 
pollen  grains  ;  w,  a  pollen  tube  which 
has  reached  and  entered  the  micropyle 
of  the  ovule ;  n,  stalk  of  o\ailc ;  o,  base 
of  the  inverted  ovule;  p,  outer 
integument  or  testa ;  q,  inner  in- 
tegument ;  /,  cavity  of  the  em- 
bryo sac ;  u,  its  basal  portion ; 
2,  oospherc. 


only  in  different  species  and 
orders,  but  throughout  the  whole  vegetable  kingdom.  And 
since  these  functions  furnish  a  more  reliable  standard  for 
judging  of  the  real  affinities  of  the  different  groups  than  do 
mere  external  resemblances,  which  are  more  liable  to  varia- 
tion and  may  often  be  accidental,  they  have  been  chosen 
by  botanists  as  the  ultimate  basis  for  the  classification  of 
plants. 

253.  Embryology.  —  The  study  of  the  developing  plantlet, 
known  as  eynbnjology,  is  a  comparatively  recent  branch  of 


THE   FLOWER  223 

science,  and  has  greatly  enlarged  our  knowledge  of  the  life 
history  of  both  plants  and  animals,  by  bringing  to  light  re- 
semblances that  exist  between  the  most  widely  divergent 
species  in  their  earlier  stages  of  development  and  thus 
showing  traces  of  a  common  origin.  It  has  shown  further, 
that  every  individual  plant  or  animal,  in  its  development 
from  the  embryo  to  the  mature  state,  passes  briefly  through 
stages  apparently  similar  to  those  which  the  species  has  trav- 
ersed in  the  course  of  its  evolution.  This  summary  repe- 
tition, by  the  individual,  of  the  evolutionary  progress  of  its 
kind  is  known  as  the  biogenetic  law,  and  through  its  intelli- 
gent application  some  of  the  most  intricate  problems  in  both 
physiology  and  psychology  have  been  solved. 

Practical  Questions 

1.  Does  the  biogenetic  law  throw  any  hght  on  the  resemblances  some- 
times observed  between  leaves  of  different  ages  in  unlike  species;  for 
example,  the  fig  and  the  mulberry?     (170;  Field  Work,  p.  195.) 

2.  Can  you  name  any  other  examples  of  plants  or  parts  of  plants  which 
show  mutual  resemblances  in  their  early  stages  that  do  not  exist  at 
maturity  ? 

3.  Are  there  other  causes  than  those  acting  under  the  biogenetic  law 
to  which  some  of  these  resemblances  may  be  referred ;  for  instance,  the 
down  and  waxy  coating  on  young  leaves  and  bud  scales?    (148,  207.) 

VI.   HYBRIDIZATION 

Material.  —  Several  potted  plants  of  tulip,  lily,  or  any  attainable 
large  flowered  kind ;  or  preferably  a  small  plot  in  a  garden  or  nursery. 

Appliances.  —  A  pair  of  dissecting  scissors,  a  camel's-hair  brush,  and 
some  paper  bags. 

Experiment  78.   Does  it  make  any  difference  whether  a  flower 

HAS  its  ovules  FERTILIZED  WITH  ITS  OWN  POLLEN  OR  WITH  THAT  OF  AN- 
OTHER FLOWER  OF  THE  SAME  KIND  ?  —  Carefully  remove  the  unopened 
anthers  from  a  bud  of  a  tulip,  or  other  large  flower  just  ready  to  unfold 
(Fig.  331),  inclose  the  mutilated  bud  in  a  small  paper  bag  until  the  stigma 
is  mature,  as  shown  by  stickiness,  then  transfer  to  it  with  a  camers-hair 
brush  some  pollen  from  another  flower.  On  the  stigma  of  a  second  flower 
of  the  same  kind  place  some  of  its  own  jwUen,  and  cover  with  a  paper  bag 
until  the  stigma  withers,  to  keep  foreign  pollen  from  reaching  it  by  means 


224 


PRACTICAL  COURSE  IN  BOTANY 


331 


332 


333 


Figs.  331-333.  —  Flower  of  Lorillard  tomato:  331,  newly  opened  bud,  showing 
stage  in  which  the  stamens  should  he  removed  ;  332,  mature  flower  :  ex,  ealyx  ;  c, 
corolla ;  s,  stamens ;  st,  stigma  ;  333,  flower  with  stamens  removed  for  pollination. 
(Natural  size.) 


of  wind  or  insects.  Watch  until  seeds  arc  matured.  Which  flower  pro- 
duces the  more  seeds  or  the  better  ones  ?  Plant  the  seeds ;  which  produce 
the  more  vigorous  progeny? 

Experiment  79.  Can  a  flower  be  fertilized  with  pollen  of  a 
DIFFERENT  KIND  ?  —  Dust  the  stigma  of  a  tuHp  or  a  Uly,  from  which  the 
stamens  have  been  removed,  with  pollen  from  a  narcissus,  iris,  or  amaryl- 
lis.     Cover  to  protect  from  wind  and  insects.     Are  any  seeds  produced  ? 

Experiments  of  this  kind,  to  be  conclusive,  ought  to  be  performed  on 
a  sufficient  number  of  plants  and  through  at  least  three  generations.  This 
is  hardly  practicable  for  class  work,  but  students  who  are  specially  inter- 
ested in  the  subject  may  carry  on  experiments  at  home,  or  supply  their 
place,  to  some  extent,  by  observations  out  of  doors,  if  there  are  any  farms 
or  gardens  accessible. 

254.  Self-fertiliza-    s^a^^ 
tion    takes    place 


when  a  stigma  is 
pollinated  from  the 
same  flower.  Hor- 
ticulturists have 
long  known  that 
continued  self- 
fertilization,  or  "in- 
breeding" as  it  is 
called  by  nursery- 
men, tends  to  dete- 
riorate a  stock ;  but 


^:> 


Q^ 


(^^       C^ 


00 


<^^ 


334 


335 


Figs.  334-335.  —  Seeds  of  Bartlett  pear,  showing 
the  advantage  of  cross-fertilization  :  334,  crow 
fertilized ;  335,  self-fertilized. 


THE  FLOWER 


226 


Fig.  336.  —  Showing  the  effect  of  in-breeding  on  corn  in  one  generation.  The 
two  left-hand  rows  are  from  self-fertilized  seed. 

Charles  Darwin  was  the  first  to  explain,  by  a  series  of  pains- 
taking experiments,  the  meaning  of  those  careful  adjustments 
which  the  more  highly  organized  plants,  as  a  rule,  have  de- 
veloped to  guard  against  it. 

255.  Cross-fertilization  is  effected  by  the  pollination  of  a 
stigma  from  another  flower  of  the  same  variety  or  species. 
As  used  by  practical  horticulturists,  the  expression  means 
that  the  two  factors,  pollen  and  ovule,  belong  to  different 
plants.  Since  pollination  is  the  necessary  antecedent  to 
fertilization,  and  the  only  means  by  which  we  can  control  it, 
the  breeder's  part  in  crossing  is  concerned  with  this  act  only 
and  nature  does  the  rest.  Darwin's  experiments  —  and  they 
are  confirmed  by  the  experience  of  plant  growers  everywhere 


226  PRACTICAL  COURSE  IN  BOTANY 

—  prove  that  the  offspring  from  crossing  different  plants  of 
the  same  kind  is  usually  stronger  and  more  productive  than 
that  from  self-fertilized  ones ;  and  if  the  parent  stocks  are 
grown  in  different  places  and  under  different  conditions,  the 
offspring  is  more  vigorous  than  that  from  the  same  kind  of 
plants  grown  under  like  conditions.  For  instance,  plants 
from  crossed  seeds  of  morning-glory  vines  growing  near  each 
other  exceeded  in  height  those  from  self-fertilized  seeds  as 
100  :  76 ;  while  the  offspring  of  plants  growing  under  different 
conditions  exceeded  those  of  the  other  cross,  in  height,  as 
100 :  78 ;  in  number  of  pods,  as  100 :  57,  and  in  weight  of 
pods,  as  100 :  51.  Knowledge  of  this  kind,  when  applied  to 
the  raising  of  fruits  and  grains  for  market,  is  of  incalculable 
value  to  gardeners  and  farmers,  and  also  to  the  amateur  who 
raises  fruits  or  flowers  for  pleasure. 

256.  Hybridization  is  the  crossing  of  two  plants  of  differ- 
ent species  or  of  widely  separated  varieties  of  the  same  species. 
The  resulting  offspring  is  a  hybrid.  Hybridization  can  take 
place  only  within  certain  limits.  If  the  species  are  too  unlike, 
the  pollen  will  either  not  take  effect  at  all,  or  the  resulting 
offspring  will  be  too  weak  and  spindling  to  live ;  or  if  they 
survive,  will  not  be  able  to  set  seed  (Exp.  79). 

257.  Effects  of  hybridization.  —  The  most  important  prac- 
tical uses  of  hybridizing  are:  (1)  it  "  breaks  the  type  "  by 
causing  plants  to  vary,  and  thus  gives  the  breeder  a  fresh 
starting  point  for  a  new  strain;  and  (2)  when  the  parent 
species  are  not  too  unlike,  it  accentuates  the  good  effects  of 
crossing,  and  sometimes  gives  rise  to  offspring  greatly  sur- 
passing either  parent  in  size  and  vigor.  In  regard  to  varia- 
bility it  may  act  in  three  ways:  (1)  the  hybrid  may  wholly 
resemble  one  parent  or  the  other,  in  which  case  there  is,  of 
course,  no  variation ;  (2)  it  may  resemble  one  parent  more 
than  the  other ;  or  (3)  it  may  show  a  blending  of  the  charac- 
ters of  the  two,  as  when  a  cross  between  a  red  poppy  and  a 
white  gives  rise  to  a  light  pink,  or  a  mixed  red  and  white 
variety.     In  the  first  two  cases,  the  characters  of  the  parent 


THE   FLOWER 


227 


Plate  11.  —  Hybrid  between  a  red  and  a  white  carnation,  showing  char- 
acters intermediate  between  the  two  parents. 


228 


PRACTICAL  COURSE  IN  BOTANY 


that  manifest  themselves  are  said  to  be  dominant;  those 
which  do  not,  recessive. 


r-fiwr^.  H 


Fig.  337.  —  Effect  of  hybridization  between  related  species  in  imparting  superior 
vigor  to  offspring  :  M,  Californian  black  wsdnut  (Juglans  call  for  nica),  male  parent; 
F,  Eastern  black  walnut  {J.  riigra),  female  parent ;  //,  hybrid. 


258.  Mendel's  Law.  —  So  long  ago  as  the  middle  of  the  last 
century  it  was  discovered  by  Gregor  Mendel,  an  Austrian 
investigator,  that  hybrids  vary  in  certain  cases  according  to 
a  fixed  law,  by  means  of  which  the  proportionate  share  of  the 
characteristics  of  the  two  parent  forms  inherited  by  the  off- 
spring can  be  foretold  with  almost  mathematical  precision. 
The  controversy  over  Darwin's  "  Origin  of  Species,"  which 
was  raging  at  the  time,  caused  Mendel's  discoveries  to  be 
overlooked  for  a  generation,  and  it  is  only  within  the  last 


DX  R 


Diagram  illustrating  Mendel's  Law. 

few  years  that  their  importance  has  been  realized.  The 
principle  of  variation  demonstrated  by  him  in  a  series  of 
experiments,  and  confirmed  by  later  investigators  is,  briefly, 


THE   FLOWER  229 

this :  If  two  parents  differing  in  some  fixed  characteristic 
be  crossed,  the  entire  offspring,  in  the  first  generation,  will  be 
like  the  parent  possessing  the  dominant  quality.  If  all  the 
seed  of  this  generation  is  planted  and  carefully  protected 
from  foreign  pollen,  its  offspring  composing  the  second 
generation  from  the  parents  will  vary  in  the  proportion  of 
I  dominants  {D,  D' ,  line  2  of  the  diagram)  to  \  recessives  {R). 
Planting  all  the  seeds  of  the  second  generation  and  carefully 
shielding  their  progeny  from  foreign  pollen,  we  get  from  D, 
line  2,  all  pure  dominants  {D,  line  3)  —  that  is,  plants  pro- 
ducing only  their  own  type,  and  from  R,  line  2,  all  pure 
recessives  {R,  line  3).  But  from  each  of  the  two  sets  of  dom- 
inants, D'D',  line  2,  marked  "  impure  "  in  the  diagram,  and 
so  called  because  their  seeds  may  produce  both  dominants 
and  recessives,  we  get  the  same  result  as  in  the  second  gen- 
eration, namely:  pure  dominants  {D'D',  line  3),  pure  reces- 
sives {R'R',  line  3),  and  impure  dominants  {D"D",  D"D",  line 
3).  If  it  were  possible  to  distinguish  the  seeds  of  these  im- 
pure dominants  before  germination  and  plant  them  only,  for 
no  matter  how  many  generations,  the  result  would  always  be 
approximately  the  same,  —  J  pure  dominants,  \  pure  reces- 
sives, and  I  impure  dominants  capable  of  producing  both 
dominants  and  recessives  in  the  proportion  of  3  :  1. 

259.  Practical  applications.  —  Four  principles  of  great 
importance  to  plant  breeders  follow  from  this  law  in  cases  to 
which  it  applies:  (1)  the  absence  of  variation  in  the  first 
generation  of  hybrids  is  no  sign  that  it  may  not  occur  later; 
(2)  pure  recessives  always  breed  true ;  hence,  if  they  show 
the  desired  character,  no  further  selection  is  necessary  for 
that  character;  (3)  pure  dominants  always  breed  true,  but 
the  distinction  between  pure  and  impure  is  usually  not 
apparent  in  one  generation;  (4)  the  descendants  of  "  im- 
pure "  parents  cannot  be  depended  upon  to  come  true  to 
either  type,  but  impure  dominants  may  breed  recessives,  and 
vice  versa,  with  the  presumption,  however,  of  3:1  in  favor 
of  dominants. 


230  PRACTICAL  COURSE   IN   BOTANY 

Practical  Questions 

1.  Would  hybridization  account  for  .some  of  the  diversities  mentioned 
in  170?     (See  257.) 

2.  To  what  cases  would  it  not  apply?     (256;  Exp.  79.) 

3.  Would  it  be  worth  while  to  try  to  hybridize  the  potato  and  squash  ? 
The  squash  and  pumpkin?  The  lily  and  rose?  Sweetbrier  and  wild 
rose  ?  Apple  and  peach  ?  Wild  crab  and  sweet  apple  ?  Blackberry  and 
strawberry?  Blackberry  and  raspberry?  Lemon  and  watermelon? 
Lemon  and  orange?  Why,  or  why  not,  in  each  ease?  (256;  Exps. 
78,  79.) 

VIL    PLANT    BREEDING 

Material.  —  If  practicable,  visit  a  market  garden,  a  florist's  establish- 
ment, or,  lacking  these,  the  fruit  and  vegetable  stalls  of  a  city  market. 

260.  Fixing  the  type.  —  It  is  the  tendency  of  plants  to 
vary  under  the  influence  of  cUmate,  soil,  food  supply,  cross- 
ing, and  other  causes  perhaps  unknown  to  us,  that  makes 
the  plant  breeder's  art  possible.  When  a  horticulturist  sets 
out  to  produce  a  new  fruit  or  vegetable,  he  first  forms  in  his 
mind  a  clear  idea  of  what  he  wants — whether  increase  of  yield 
or  size,  resistance  to  cold,  drought,  or  disease,  improvement  in 
flavor,  color,  shape,  etc.,  or  change  in  the  time  of  maturing  or 
flowering  (early  and  late  varieties).  Suppose,  for  instance, 
he  wishes  to  produce  an  oxeye  daisy  with  all  the  disk  florets 
changed  to  white  ones  like  the  rays.  He  will  begin  by  selecting 
plants  with  the  greatest  number  of  rays  and  the  most  conspic- 
uous ones  that  he  can  find,  and  sowing  the  seeds  of  the  flowers 
which  show  the  greatest  tendency  to  the  development  of  these 
qualities.  He  will  continue  this  process  from  generation  to 
generation,  rigorously  destroying  all  specimens  that  do  not 
approach  nearer  the  ideal  sought,  until  all  disposition  to 
"  rogue,"  as  the  tendency  to  revert  is  called,  has  been  elimi- 
nated. When  variations  cease  to  occur  and  the  seed  of  the 
new  variety  always  "  come  true,"  the  type  is  said  to  be  fixed; 
though  some  care  will  always  be  necessary  to  keep  it  so, 
as  the  influence  of  changed  surroundings  and  the  danger  of 
mixture  with  foreign  pollen  must  always  be  provided  against. 


THE  FLOWER 


231 


261.  Survival  of  the  fittest.  —  In  the  fierce  struggle 
continually  going  on  among  both  plants  and  animals  for 
food,  shelter,  and  elbow  room  in  the  world,  any  indi- 
vidual that  happens  to  vary  in  a  way  which  adapts  it  to 

its    surroundings    a  

little  better  than  its 
rivals,  has  an  advan- 
tage that  will  enable 
it  to  survive  when 
less  favored  mem- 
bers of  the  species 
will  perish.  Its  off- 
spring, or  some  of 
them,  may  inherit 
this  quality  and 
transmit  it,  with  the 
attendant  advan- 
tage, to  their  poster- 
ity, and  so  on,  till 
that  particular 
breed  outstrips  all 
competitors,  and  in 
time,  as  the  less  fa- 
vored intervening 
forms   die   out,    be- 

'  seea. 

comes  differentiated 

as  a  new  species.     This  is,  in  brief,  the  doctrine  of  natural 

selection  and  the  survival  of  the  fittest. 

262.  Artificial  selection.  —  Artificial  selection  enables  the 
breeder  to  accomplish  more  quickly  what  nature  appears  to 
do  by  the  slow  process  of  natural  selection.  It  is  by  this 
means  that  our  choicest  fruits  and  vegetables  have  been  de- 
veloped from  greatly  inferior,  and  sometimes  inedible,  wild 
forms.  Plants  respond  so  readily  to  the  influence  of  selec- 
tion, and  the  changes  brought  about  by  it  are  so  rapid, 
that  new  styles  of  fruits  and  flowers  succeed  each  other  in 


F£G.  338.  —  A  field  of  pumpkins  grown  from  selected 


232  PRACTICAL  COURSE   IN   BOTANY 

the  market  with  ahnost  as  great  frequency  and  in  as  ready- 
response  to  demand  as  the  new  styles  of  women's  bonnets 
and  gowns  in  the  shop  windows. 

263.  Causes  of  variation.  —  While  man  cannot  directly 
force  plants  to  vary  in  any  given  direction,  he  can  hasten  the 
process  of  variation  by  crossing,  or  by  changing  the  conditions 
under  which  they  are  growing.  This  is  called  "  breaking 
the  type."  Hybridization  furnishes  the  readiest  means  to 
this  end.  Change  of  food  supply,  especially  if  accompanied 
by  excess  of  nourishment,  is  probably  the  expedient  that 
ranks  next  in  effectiveness.     Light,  temperature,  moisture, 


Fig.  339.  —  Variation  in  blackberry  leaves  due  to  hybridization. 

character  of  the  soil,  exposure  to  wind,  and  the  like,  also 
have  their  influence;  and  in  adapting  themselves  to  changes 
in  these  various  conditions,  plants  are  apt  to  exhibit  an 
unusual  number  of  variations,  when  removed  from  one  local- 
ity to  another,  especially  if  the  difference  in  soil  and  climate 
is  very  marked.  Now  comes  the  breeder's  opportunity.  By 
taking  advantage  of  such  variations  as  may  occur  either 
spontaneously,  or  as  the  result  of  his  efforts  to  break  the  type, 
he  will  generally  find  some  that  will  meet  his  requirements; 
and  knowing  the  effect  produced  by  different  conditions,  he 
can,  to  a  certain  extent,  influence  the  course  of  variation  in 
the  direction  desired,  by  subjecting  his  specimens  to  the 


THE  FLOWER 


233 


conditions  that  tend  to  produce  it.  If  he  wishes  to  develop 
a  dwarf  variety,  for  instance,  he  will  take  notice  that  over- 
crowding, lack  of  nourishment,  and  cold  tend  to  produce  that 
result  in  nature,  and  by  acting  on  this  hint  he  can  direct  his 
efforts  more  intelligently.  He  will  learn,  too,  not  to  waste 
time  in  trying  to  breed  a  plant  contrary  to  its  nature.  He 
must  not  expect  to  gather  figs  from  thistles  by  any  art  of 
selection  or  skill  in  culture.  By  attention  to  Mendel's  law, 
a  still  further  saving  of  time  and  labor  may  be  effected. 

It  is  obvious,  from  what  has  been  said,  that  a  breeder's 
chance  of  finding  what  he  wants  will  be  greater  in  proportion 
to  the  number  of  individual  plants  he  has  to  choose  from. 
For  this  reason,  a  horticulturist  sometimes  uses  thousands 
and  hundreds  of  thousands  of  specimens  of  a  single  kind  in 
conducting  his  experiments.  In  this  way  he  compresses  into 
a  short  space  of  time  the  advantage  that  nature  can  gain  only 
by  spreading  her  random  experiments  over  a  long  series  of 
years,  or  even  centuries. 

264.  Mutation  and  variation.  —  There  are  at  least  two 
ways  in  which  changes  in  vegetable  and  animal  forms  are 
thought  to  occur:  (1) 
by  the  preservation  and 
fixation  through  selec- 
tion and  heredity,  of 
slight  differences  that 
may  appear  from  time  to 
time,  such  divergences 
being  called  "fluctuat- 
ing variations"  ;  (2)  by 
the  appearance  now  and 
then,  due  to  causes  as 
yet  unknown,  of  definite 
and  sudden  changes 
creating  a  new  form  at 

a  single,  though  perhaps  small,  leap.  ^Yhen  such  a  change 
is  temporary  and  passes  away  with  the  individual  in  which 


Fig.  340. —  Mutation  in  twin  cars  of  corn, 
showing  the  sudden  variations  that  sometimes 
occur,  by  wnich  a  new  type  may  be  provided 
without  the  hibor  of  selection. 


234  PRACTICAL   COURSE   IN   BOTANY 

it  first  appeared,  it  is  called  a  "  sport,"  and  leads  to  no 
important  results;  but  when  it  is  inherited  by  the  offspring, 
so  that  it  is  capable  of  giving  rise  to  a  new  species,  it  con- 
stitutes a  "  mutation."  The  value  of  a  mutation  to  breeders 
in  saving  time  and  trouble  is  obvious.  Professor  Hugo  de 
Vries,  a  Dutch  botanist,  was  the  first  to  call  attention  to  the 
importance  of  mutation  and  its  bearing  upon  the  production 
of  new  species. 

265.  Factors  in  the  evolution  of  species.  —  Variation, 
heredity,  and  selection  are  the  three  principal  agents  under- 
lying all  changes,  whether  for  the  improvement  or  deteriora- 
tion of  living  organisms.  The  influence  of  external  surround- 
ings in  keeping  up  a  variation  once  begun,  or  in  starting  new 
ones,  is  also  a  factor  that  cannot  be  disregarded.  It  is  for 
this  reason  that  natural  species  are  so  much  more  stable  than 
those  brought  about  by  man.  The  former,  being  evolved  in 
response  to  natural  conditions,  are  liable  to  change  only  as 
alterations  in  their  surroundings  are  brought  about  by  the 
slow  operation  of  natural  causes.  But  the  types  resulting 
from  the  breeder's  art,  produced  as  they  often  are  in  response 
to  human  demands  and  in  direct  opposition  to  the  require- 
ments of  natural  conditions,  are  in  a  sense  purely  artificial,  and 
can  be  preserved  only  by  keeping  up  the  artificial  surround- 
ings by  which  they  were  developed.  Hence,  the  importance 
of  diligent  cultivation  and  constant  care  and  tillage,  without 
which  the  most  carefully  selected  stocks  may  quickly  "  run 
out  "  and  degenerate  into  worthless  forms. 

Practical  Questions 

1.  Which  are  the  more  pliable  to  the  breeder's  art,  annuals  or  peren- 
nials?    Why?     (91,93,262,263.) 

2.  What  advantage  is  gained  by  using  buds  and  grafts  instead  of 
seedlings  in  making  new  varieties  of  fruit  trees?     (257,  259,  260.) 

3.  Would  it  be  practicable  to  breed  new  varieties  of  slow-growing  forest 
trees,  like  oak,  cypress,  redwood,  from  seeds  ?  Why  or  why  not  ?  (93, 
262,  263.) 

4.  Can  you  account  for  the  existence  of  the  numerous  intermediate 
forms  between  the  different  species  of  oaks  found  in  nature?    (255,  257.) 


THE   FLOWER  235 

5.  If  a  breeder  wished  to  produce  a  sweet-scented  daisy  or  pansy,  how 
would  he  make  his  selections?     (260.) 

6.  Which  would  he  the  more  useful  for  his  purpose,  a  plant  that  showed 
a  general  tendency  to  variability,  or  one  that  remained  steadily  fixed  to 
its  type?     (260.) 

7.  What  could  he  do  to  break  the  type  ?     (263.) 

8.  Would  an  intelligent  breeder  set  out  to  produce  edible  roots  and 
tubers  from  wheat  or  barley?     (263.) 

9.  Would  he  think  it  worth  while  to  try  to  develop  a  fleshy  fruit  from 
a  filbert  or  a  walnut  tree  ?  From  a  haw  ?  From  sheepberry  and  black 
haw?     From  tupelo  (ogeechee  lime)  ?     (263.) 

10.  Suppose  a  florist  should  wish  to  change  the  color  of  a  rose  from  pink 
to  deep  red ;  how  could  he  hasten  the  process  ?     (257,  263.) 

11.  Explain  why  it  is  so  much  easier  to  produce  new  varieties  of  plants 
when  there  are  already  many  kinds  in  existence,  as,  for  example,  the  rose, 
peach,  and  chrysanthemum.     (255,  256;  Exps.  78,  79.) 


VIII.    ECOLOGY    OF    THE    FLOWER 

A.   The  Prevention  of  Self-pollination 

Material.  —  Any  kind  of  unisexual  flowers  obtainable.  Some  good 
examples  for  illustrating  points  mentioned  in  the  text  are  :  for  spring  and 
early  summer,  catkins  of  almost  any  of  our  common  forest  trees,  —  oak, 
hickory,  willow,  poplar,  etc.;  tassels  and  young  ears  of  early  corn;  for 
summer  and  early  fall,  flowers  of  late  corn,  and  of  melon,  squash,  pump- 
kin, or  others  of  the  gourd  family.  Examples  of  dichogamy  are  :  evening 
primrose,  showy  primrose  {Oenothera  speciosa),  willow  herb  (Epilobium), 
dandelion,  artichoke,  sunflower,  or  any  of  the  composite  family;  of  dimor- 
phism: English  primrose  (Primula),  loosestrife  (Pulmonaria),  bluets 
(Houstonia),  partridge  berry;  cleistogamic:  fringed  polygala,  violets. 
Peanuts,  while  not  technically  classed  as  cleistogamic,  are  strictly  close- 
fertilized,  and  approach  the  type  so  nearly  that  they  may  be  used  as  an 
illustration. 

266.  Ecology  is  the  study  of  plants  and  animals  in  relation 
to  their  surroundings.  The  principal  modifications  that 
flowers  undergo  in  this  respect  are  in  adapting  themselves 
for  (1)  pollination,  and  (2)  protection. 

267.  Unisexual  flowers.  —  The  advantages  of  cross  fer- 
tilization were  shown  in  the  last  two  sections.     It  was  also 


236 


PRACTICAL  COURSE  IN  BOTANY 


341  342 

Figs.  341,342.— 
Unisexual  flowers  of  wil- 
low :  341,  staminate; 
342,  pistillate. 


shown  that  the  first  step  taken  by  the  breeder  to  secure  this 
result  is  to  render  the  flower  incapable  of  self-fertilization, 
by  removing  the  stamens.  Nature  ac- 
complishes the  same  purpose  ])y  the  more 
effectual  expedient  of  providing  imper- 
fect, or  unisexual  flowers,  in  which  sta- 
mens only,  or  pistils  only,  occur  in  the 
same  flower.  When  the  stamens  alone 
are  present,  the  flower  is  said  to  be  stam- 
inate, or  sterile,  because  it  is  incapable 
of  producing  seeds  of  its  own,  though  its 
pollen  is  a  necessary  factor  in  seed  pro- 
duction. If,  on  the  other  hand,  the 
ovary  is  present  and  the  stamens  absent, 
the  flower  is  pistillate  and  fertile ;  that  is,  capable  of  produc- 
ing fruit  when  impregnated  with  pollen.  Sometimes  both 
stamens  and  pistils  are  wanting,  as 
in  the  showy  corollas  of  the  garden 
"snowball,"  the  hydrangea,  and 
the  rays  of  the  sunflower.  Such 
blossoms:  are  said  to  be  neutral, 
from  the  Latin  word  neuter,  mean- 
ing neither,  because  they  have 
neither  pistils  nor  stamens.  They 
can,  of  course,  have  no  direct  part 
in  the  production  of  fruit,  but  are 
for  show  merely.     (231.) 

268.  Moncecious  and  dicecious 
plants.  —  When  both  kinds  of 
flowers,  staminate  and  pistillate, 
are  borne  on  the  same  plant,  as  in 
the  oak,  pine,  hickory,  and  most  of 
our  common  forest  trees,  they  are 
said  to  be  monoecious,  a  word  which 
means  "  belonging  to  one  household";  when  borne  on  sepa- 
rate plants,  as  in  the  willow,  sassafras,  and  black  gum,  tliey 


Fig.  343.  —  Twig  of  oak  with 
both  kinds  of  flowers  :  /,  fertile 
flowers ;  s,  s,  staminate ;  a,  pis- 
tillate flower,  enlarged  ;  b,  verti- 
cal section  of  pistillate  flower, 
enlarged  ;  c,  portion  of  one  of  the 
sterile  aments,  enlarged,  showing 
the  clusters  of  stamens. 


THE   FLOWER 


237 


344  345 

Figs.  344,  345.  —  Flower  of  fireweed  {Epilohium  an- 
gustifolium)  :  344,  with  mature  stamens  and  immature 
pi3til ;  345,  the  same  a  few  days  older,  with  expanded 
pistil  after  the  anthers  have  shed  their  pollen.  (After 
Grav.) 


are  dioecious,  or  "  of  two  households."  Draw  a  flowering  twig 
of  oak,  pine,  or  willow.  Where  are  the  fertile  flowers  situated  ? 
Notice  how  very  much  more  numerous  the  staminate  flowers 
are  than  the  fertile  ones.     Why  is  this  necessary  ?     (275.) 

269.  Dichogamy  is  the  name  applied  to  a  condition  where 
the  stamens  and 
pistils  mature  at 
different  times, 
as  in  the  evening 
primrose,  oxeye 
daisy,  and  most 
of  the  composite 
family.  It  is  a 
very  common 
method  in  nature 
for  preventing 
self-pollination,  and  quite  as  effective  as  the  monoecious 
arrangement,  since  it  renders  the  flowers  practically  unisexual. 

270.  Dimorphism  denotes  a  condition  in  which  the  sta- 
mens and  pistils  are  of  different  relative  lengths  in  different 
flowers  of  the  same  species,  the  stamens  being  long  and  the 

pistils  short  in  some,  the  pistils 
long  and  the  stamens  short  in 
others.  Flowers  of  this  sort  are 
said  to  be  dimorphous,  or  dimor- 
phic,  that  is,  of  two  forms ;  and 
some  species  are  even  trimor- 
phic,  having  the  two  sets  of 
organs  long,  short,  and  medium, 
respectively,  in  different  indi- 
viduals. Examples  of  dimorphic  flowers  are  the  pretty  little 
bluets  {Houstonia  ccprulea),  the  partridge  berry,  the  swamp 
loosestrife,  and  the  English  cowslip.  Of  trimorphic  flowers 
we  have  examples  in  the  wood  sorrel  and  the  spiked  loosestrife 
(Lythrum  salicaria)  of  the  gardens.  These  flowers  were  a 
great  pu2zle  to  botanists  until  the  celebrated  naturalist, 


346  347 

Figs.  346-347.  —  Flower  of  pul- 
monaria  :  346,  long  styled  ;  347,  short 
styled. 


238 


PRACTICAL  COURSE  IN  BOTANY 


348  349  349 

Figs.  348-350.  —  Three  forms  of  loosestrife  {Lyth- 
rum  salicaria). 


Charles  Darwin, 
proved  by  experi- 
ment that  the  seeds 
produced  by  polH- 
nating  a  dimorphous 
flower  with  its  own 
pollen,  or  with  pol- 
len from  a  flower  of 
similar  form,  are  of 
very  inferior  quality 
to    those    produced 

by  impregnating  a  long-styled  flower  with  pollen  from  a 

short-styled  one,  and  vice  versa. 

271.  "Nature  abhors  self-fertilization."  —  These  are  the 
three  principal  methods  by  which  nature  provides  against 
self-fertilization.  Other  cases  occur  in  which  the  relative 
position  of  the  two  organs  is  such  that  self-pollination  is 
difficult,  or  impossible,  as  in  the  iris  and  bear's  grass  ;  or  the 
pollen  may  be  incapable  of  acting  on  the  stigma  of  the  flower 
that  produced  it.  This  aversion  to  self-fertilization  is  so 
great  that  many  flowers,  even  when  capable  of  it,  will  give 
preference  to  the  pollen  of  another  plant  of  the  same 
kind,  if  dusted  with  both.  From  his  observations  on  the 
behavior  of  plants  in  reference  to  this  function,  Charles  Dar- 
win drew  the  conclusion  that  "Nature  abhors  perpetual 
self-fertilization." 

272.  Cleistogamic  flowers. — ^  Apparent  exceptions  to  this 
rule  are  the  hidden  flowers  found  on  certain  plants  which 
seem  to  have  been  constructed  with  a  special  view  to  self- 
fertilization.  They  are  called  cleistogamic,  or  closed,  because 
they  never  open,  but  are  fertilized  in  the  bud;  and  those  of 
the  fringed  polygala  do  not  even  rise  above  ground  at  all. 
Flowers  of  this  kind  can  be  found  on  several  species  of 
violet,  concealed  under  the  leaves,  close  to  the  ground ;  and 
the  flowers  of  the  peanut,  found  in  the  same  situation,  while 
they  open  slightly,  are  close-fertilized  and  practically  cleisto- 


THE  FLOWER  239 

gamic.  They  are  much  more  prolific  than  ordinary  flowers, 
but  are  not  common,  and  seem  to  be  a  provision  against 
accident,  for  the  plants  producing  them  are  generally  pro- 
vided with  other  flowers  of  the  usual  kind,  —  some,  as  the 
violet,  having  elaborate  special  adaptations  for  cross  fertili- 
zation. 

Practical  Questions 

1.  "Why  does  a  strawberry  bed  sometimes  fail  to  fruit  well,  although  it 
may  flower  abundantly?     (267,  268.) 

2.  Are  berries  found  on  all  sassafras  trees?  On  all  buckthorns? 
HoUies  ? 

3.  Would  a  solitary  hop- vine  produce  fruit?  A  solitary  ash  tree? 
(267.) 

4.  "Wliy  is  a  mistletoe  bough  with  berries  on  it  so  much  harder  to  find 
than  one  with  foliage  merely  ?     (267,  268.) 

B.   Wind  Pollination 

Material,  —  In  spring,  catkins  of  forest  trees,  staminate  and  pistillate 
flowers  of  pine.  At  nearly  all  seasons,  heads  of  grain  and  panicles  of  va- 
rious kinds  of  grass  can  be  obtained.  For  experiment,  a  potted  plant  of 
any  kind,  just  about  to  bloom,  may  be  used. 

Experiment  80.  To  test  the  effect  of  shutting  out  external 
AGENCIES.  —  Tie  paper  bags  over  flower  buds  of  different  kinds  when  nearly 
ready  to  open  and  leave  until  the  flowers  have  withered.  On  removing 
the  bags,  mark  with  colored  threads  the  flowers  that  had  been  covered,  and 
watch  until  seed  time.  Do  you  notice  any  difference  in  the  number,  size, 
or  weight  of  the  seed  produced  by  them  and  by  those  of  the  same  kind  left 
exposed  ?  How  do  you  account  for  the  diff"erence,  if  there  is  any  ?  By 
what  agencies  could  foreign  j^oUen  have  been  carried  to  the  stigmas  of 
the  exposed  flowers?  If  any  of  the  covered  specimens  wither  and  drop 
their  seed  vessels  without  any  attempt  to  fruit,  examine  a  fresh  flower,  and 
see  if  it  is  capable  of  self-pollination. 

As  already  explained,  experiments  of  this  kind,  to  be  conclusive,  should 
be  tried  on  as  many  specimens  as  possible.  The  greater  the  number  of 
species  and  individuals  included,  the  better.  Where  it  is  not  practicable 
to  carry  on  experiments  by  the  class,  pupils  who  are  interested  can  make 
them  at  home. 

273.  The  problem  of  pollination.  —  'WHien  a  plant  has  pro- 
vided against  self-pollination,  its  problem  is  only  half  solved, 


240 


PRACTICAL  COURSE  IN  BOTANY 


as  it  must  now  depend  upon  the  conveyance  of  pollen  to  the 
stigma  by  extraneous  means. 

274.  Adaptations  to  wind  pollination.  —  A  very  large 
number  of  plants,  among  which  are  included  nearly  all  our 

principal  forest  trees,  grains, 
and  grasses  of  every  kind, 
depend  exclusively  upon  the 
wind  for  the  distribution  of 
their  pollen.  This  being 
the  case,  it  is,  of  course,  an 
advantage  to  them  to  get 
rid  of  all  unnecessary  ap- 
pendages that  might  hinder 
a  free  play  of  the  wind 
among  their  flowers,  and  so 
they  consist,  as  a  rule,  of 
essential  organs  only  (Figs. 
34 1 ,  342) .  Such  flowers  are 
often  distinguished,  how- 
ever, especially  among 
grasses  and  low  herbs,  by 
large,  feathery  stigmas  that 
are  well  adapted  to  catch  and  hold  any  stray  pollen  grains 
which  may  be  floating  in  the  air.  Place  a  stigma  of  oat  or 
other  grass  under  the  microscope  and  you  will  probably  see 
a  number  of  pollen  grains  clinging  to  its  branches. 

275.  The  disadvantages  of  wind  pollination.  —  This  is  a 
very  clumsy  and  wasteful  method,  however,  for  so  much 
]:>()llen  is  lost  by  the  haphazard  mode  of  distribution  that  the 
plant  is  forced  to  spend  its  energies  in  producing  a  vast 
amount  more  than  is  actually  needed,  and  great  masses  of  it 
are  frequently  seen  in  spring  floating  like  patches  of  suli)hur 
on  ponds  and  streams  in  the  neighborhood  of  pine  thickets. 
Like  those  that  are  self-pollinated,  wind-pollinated  flowers 
are  generally  very  inconspicuous,  devoid  of  odor,  and  of  all 
attractions  of  form  or  color^  because  they  have  no  need  of 


Fig.  351.  —  Feathery  stigmas  of  a  grass 
adapted  to  wind  pollination. 


THE   FLOWER  241 

these  allurements  to  attract  the  visits  of  insects.  Besides 
being  wasteful,  wind  pollination  is  very  uncertain.  The 
pollen  cannot  be  blown  about  very  well  unless  it  is  dry,  and 
in  rainy  weather  it  may  all  be  rotted  or  washed  away  before 
it  can  reach  the  stigmas  that  are  ready  to  receive  it. 

Practical  Questions 

1.  Why  do  the  flowers  of  oak,  willow,  and  other  wind-fertilized  plants 
generally  appear  before  the  leaves?     (274.) 

2.  Can  you  account  for  the  showers  of  "sulphur"  sometimes  reported 
in  the  newspapers  ?     (275.) 

3.  Do  you  see  any  connection  between  the  feathery  stigmas  of  most 
grasses  and  their  mode  of  pollination?     (274.) 

4.  Why  are  house  plants  not  apt  to  seed  so  well  as  those  left  in  the 
open?     (Exp.  80.) 

5.  Why  are  the  tassels  of  corn  placed  at  the  tip  of  the  stalk?     (274.) 

6.  Can  you  trace  any  connection  between  the  winds  and  the  corn  crop  ? 
(274.) 

7.  If  March  winds  should  cease  to  l)low,  would  vegetation  be  affected 
in  any  way?     (274.) 

8.  Why  are  wind-fertilized  plants  generally  trees  or  tall  herbs  ?     (274.) 

9.  Is  it  good  husbandry  to  plant  different  varieties  of  corn  or  other 
grain  in  the  same  field,  if  :*  is  desired  to  keep  the  strain  pure  ?    (255,  274.) 

10.  Is  water  a  good  pollen  carrier  ?     (275.) 

11.  What  is  the  only  class  of  plants  it  is  likely  to  reach? 

12.  What  is  the  only  other  agency,  besides  wind  and  water,  by  which 
this  office  can  be  performed  ? 

C.   Insect  Pollination 

M.\TERiAL.  —  Half  a  dozen  panes  of  glass,  about  6X9;  squares  of 
bright-colored  cloth  or  paper;  a  few  spoonfuls  of  honey  or  sirup;  per- 
fumes of  various  kinds,  preferably  flower  extracts ;  fetid  and  disagreeable 
smelling  substances,  such  as  a  bit  of  decaying  animal  or  vegetable  matter. 
Observations  on  living  plants  can  best  be  made  out  of  doors  or  in  a  green- 
house, as  opportunity  offers. 

Experiment  81.  Has  the  color  of  flowers  any  attraction  for 
INSECTS  ?  —  Place  half  a  dozen  panes  of  ordinary  window  glass  out  of  doors 
or  in  an  open  window  to  which  insects  can  have  free  access.  Lay  under 
the  first  pane  a  piece  of  black  paper  or  cloth,  and  under  the  otlu^vs  bright- 
colored  pieces  of  red,  blue,  white,  yellow,  and  purple.  Drop  on  the  center 
of  each  pane  a  little  honey  or  sirup,  and  watch.  Do  in.sects  show  any 
color  preferences?    Which  color  attracts  fewest  visitors?    Which  most? 


242  TRACTTCAL  COURSE   TN   BOTANY 

Experiment  82.  Does  odor  influence  insects  ?  —  Try  the  same 
experiment  with  different  odors,  removing  the  bright  colors  and  sprink- 
Ung  some  kind  of  perfume  on  each  pane.  Try  also  tlic  effect  of  decay- 
ing meat  and  other  malodorous  substances.  Are  any  insects  attractetl  by 
these  ?  What  kinds  ?  Does  this  account  for  the  noisome  smells  of  the 
"  carrion-flower  "  and  skunk  cabbage  ?  What  kinds  of  insects  are  attracted 
by  sweet-smelling  substances  ?  Do  the  greater  number  appear  to  be  at- 
tracted by  these,  or  by  foul  odors?  Are  flowers  of  the  sweet-smelling 
or  the  foul-smelling  kind  more  common  in  nature  ?  Do  insects  seem  to 
be  more  strongly  influenced  by  colors  or  by  odors  ? 

276.  The  color  of  flowers,  being  an  adaptation  to  changing 
external  conditions,  is  a  very  unstable  quality,  and  varies 
greatly  within  the  limits  of  the  same  species.  Even  on  the 
same  stem,  flowers  of  different  colors  are  often  found,  due, 
probably,  to  hybridization.  Yet,  notwithstanding  all  this 
apparently  random  intermingling  of  hues,  the  range  of  color 
for  each  species  is  confined,  approximately,  within  certain 
limits.  Nobody  has  ever  seen  a  blue  rose  or  a  yellow  aster; 
and  though  the  florist's  art  is  constantly  narrowing  the  ap- 
plication of  this  law,  it  still  remains  true  that  in  a  state  of 
nature,  certain  colors  seem  to  be  associated  together  in  the 
floral  art  gamut.  Yellow  is  considered  the  simplest  and 
most  primitive  color  in  flowers,  and  blue  the  latest  and 
most  highly  evolved.  Yellow,  white,  and  purple,  in  the 
order  named,  are  the  commonest  flower  colors  in  nature ; 
blue,  the  rarest.  Do  you  see  any  relation  between  these  facts 
and  the  color  preferences  of  insects  ? 

277.  Advantages  of  insect  pollination.  —  It  is  evident  that 
this  is  a  much  more  certain  as  well  as  a  more  economical 
method  of  securing  polhnation  than  through  the  haphazard 
agency  of  wind  or  water.  In  probing  around  for  the  nectar 
or  the  pollen  upon  which  they  feed,  these  busy  little  creatures 
get  themselves  dusted  with  the  fertilizing  powder,  which  they 
unconsciously  convey  from  the  stamen  of  one  flower  to  the 
pistil  of  another.  Insects  usually  confine  themselves,  as  far 
as  possible,  to  the  same  species  during  their  day's  work,  and 
since  less  pollen  is  wasted  in  this  way  than  would  be  done  by 


THE   FLOWER 


243 


the  wind,  it  is  clearly  to  the  advantage  of  a  plant  to  attract 
such  visitors,  even  at  the  expense  of  a  little  honey,  or  of  a 
liberal  toll  out  of  the  pollen  they  distribute. 

278.  Special  partnerships.  —  Some  plants  have  adapted 
themselves  to  the  visits  of  one  particular  kind  of  insect  so 
completely  that  they  would  die  out  if  that 
species  were  to  become  extinct.  The  well- 
known  alliance  between  red  clover  and  the 
bumblebee  was  brought  to  light  when  the 
plant  was  first  introduced  into  Australia. 
It  grew  luxuriantly  and  blossomed  pro- 
fusely, but  would  never  set  seed  till  the 
bumblebee  was  introduced  to 
keep  it  company. 

A  remarkable  partnership  of 
this  kind  exists  between  the 
pronuha,  or  yucca  moth,  and 
the  flowering  yuccas,  of  which  the  bear's  grass 
and  Spanish  bayonet  are  familiar  examples. 
The  pods  of  these  plants  are  never  perfect,  but 
all  show  a  constriction  at  or  near  the  middle, 

such  as  is  some- 


FiG.  352.  —  Pod 
of  yucca  pierced  by 
the  Pronuba  yuc- 
casella. 


seen    m 

sides     of 

plums 

pears. 


Fig.  353.— 
Pronuba  polli- 
nating pistil  of 
yucca. 


Fig. 


354.  —  Moth  resting  on  yucca 
blossom. 


This  is  caused  by  the  larvae 
of  the  moth,  which  feed  upon 
the  unripe  seeds.  A  glance 
under  the  nodding  perianth 
of  a  yucca  blossom  (Fig.  354) 
will  show  that  the  short  stamens  are  curved  back  from  the 
pistil  in  such  a  manner  that,  under  ordinary  circumstances, 
the  pollen  cannot  reach  the  stigma  except  by  the  rarest 
accident.  But  the  yucca  moth,  as  soon  as  she  has  deposited 
her  eggs  in  the  seed  vessel,  takes  care  to  provide  a  crop  of 


244 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  355.  —  Upper  boughs  of  a  capri- 
fig  tree,  showing  an  abundant  crop  of 
spring  fruit. 


food  for  her  offspring  by  gathering  a  ball  of  pollen  in  her 
antenna?  and  deliberately  plastering  it  over  the  stigma  (Fig. 
353).  In  this  way  fertilization  of  the  ovules  and  maturing 
of  the  fruit  is  secured.     The  larva?  feed  on  the  unripe  seeds 

for  a  time,  but  so  few  are 
destroyed  in  proportion  to 
the  number  matured  that 
the  plant  can  well  afford  to 
pay  the  small  toll  charged 
in  return  for  the  service 
rendered. 

279.  Caprification  of  the 
fig.  —  A  more  complicated 
case  of  specialization  is  that 
of  the  Smyrna  fig  of  com- 
merce —  the  only  one  of  the 
species  that  is  capable  of 
perfecting  seeds.  The 
staminate  flowers  are  borne  on  a  separate  tree,  the  caprifig, 
which  grows  wild  in  the  countries  bordering  on  the  Medi- 
terranean. The  caprifigs,  as  the  fruit  of  this  tree  is  called, 
are  worthless  except  as  the  breeding 
and  nesting  places  of  a  small  insect, 
the  fig  wasp.  This  insect  is  the 
necessary  agent  in  conveying  pollen 
from  the  stamens  of  the  caprifig  to 
the  pistils  of  the  Smyrna  fig,  which  it 
penetrates  at  certain  seasons  of  the 
year  in  the  effort  to  lay  its  eggs.  In 
order  to  insure  caprification,  as  this  process  is  called,  the 
caprifigs  are  strung  by  hand  on  fillets  of  cord  or  raffia  and 
hung  about  on  the  trees  which  are  to  be  fertilized.  In  this 
case  we  have  an  example  of  a  threefold  partnership  between 
man,  the  fig  tree,  and  the  wasp,  which  is  necessary  to  the 
existence  of  two  of  the  parties. 


Fig.  356. — Female  wasps 
issuing  from  the  galls  of  capri- 
figs, in  which  the  eggs  are 
laid. 


THE  FLOWER 


24^ 


D.    Protective  Adaptation 

Experiment  83.  Are  the  floral  envelopes  op  any  use  ?  —  Care- 
fully remove  the  calyx  and  corolla  from  a  young  flower  bud  on  a  growing 
plant  and  see  what  will  happen.  Remove  them  from  a  flower  just  unfold- 
ing. Mark  each  by  tying  a  colored  thread  lightly  around  the  petiole  and 
see  if  it  sets  as  many  seeds,  or  as  good  ones,  as  the  unmutilated  flowers  on 
the  same  plant. 

Experiment  84.  Is  the  position  of  a  flower  on  the  stem  of  any 
importance  ?  —  Invert  a  blossom  of  pea  or  sage,  and  see  what  parts  would 
come  in  contact  with  the  body  of  a  visiting  insect.  How  would  its  chances 
for  pollination  be  affected?  Try  to  make  a  flower  grow  in  an  inverted 
position  by  tying  or  weighting  it  down,  and  watch  the  effect  on  seed  pro- 
duction. 

Experiment  85. 
BY  light  ?  —  Place 
window  so  that  the 
position  of  the  buds. 
to  light,  and  watch 

Experiment  86. 
BY  GEOTROPiSM  ?  —  Lay  a  potted  plant  of  lily  of  the  valley,  larkspur. 


Is  THE  position  OF  FLOWERS  ON  THE  STEM  INFLUENCED 

a  potted  plant  with  expanding  flower   buds  near  a 
light  will  reach  it  from  one  side  only,  and  notice  the 
After  a  day  or  two  reverse  the  position  with  regard 
whether  any  change  of  position  takes  place. 

Is  THE  POSITION  OF  FLOWERS  ON  THE  STEM  INFLUENCED 


357 


358 


Figs.  357-359.  —  Flower  of  monkshood,  showing  the  changes  hy  which  it  returns 
to  its  original  position  under  the  influence  of  geotropism  after  the  axis  of  inflorescence, 
s,  has  been  inverted:  357,  inverted  position;  358,  change  due  to  negative  geotro- 
pism ;  359,  change  due  to  lateral  geotropism. 

gladiolus,  or  digitalis  in  a  horizontal  position,  tie  the  main  stem  to  keep 
it  from  changing  its  direction  of  growth,  and  leave  for  two  or  three  days 
iin  a  place  where  it  is  lighted  equally  on  all  sides.  How  do  the  individual 
flowers  behave  ?    What  part  bends  to  turn  them  up  ?    Vary  the  experi- 


246 


PRACTICAL   COURSE   IN   BOTANY 


360 


Figs.  360,  361.  —  Protection  of  pollen  in  the 
thistle:  360,  position  at  night,  or  during  wet 
weather  ;  361,  position  in  sunshine. 


ment  by  turning  the  pot  bottom  upwards  so  that  the  flowering  axis  will 
point  downwards.  This  can  be  done  by  inclosing  the  pot  in  a  bag  of  strong 
cheesecloth,  with  the  string  tied  loosely  but  firmly  around  the  foot  of  the 
stem  to  prevent  the  contents  from  falling  out,  and  suspending  the  whole 
bottom  upwards.  In  making  these  experiments,  use  flowers  that  grow 
in  a  long  cluster,  or  raceme,  and  hold  the  main  axis  in  a  vertical  position 
by  tying  or  weighting  it  down.  Watch  the  behavior  of  the  individual 
flowers.     Arrange  another  pot  containing  the  same  kind  of  plant,  in  the 

same  way,  and  suspend  one 
361  in  a  dark  place,  keeping  the 

other  in  the  light.  Does  the 
same  movement  take  place  in 
both?  Is  it  in  response  to 
light,  or  to  gravity  ? 

280.  Means  of  pro- 
tection. —  Where  plants 
have  adapted  them- 
selves to  insect  polli- 
nation, it  is,  of  course,  important  to  shut  out  intruders  that 
would  not  make  good  carriers.  In  general,  small,  creeping 
things,   like   ants   and         ^r^  -^ 

plant  lice,  are  not  such  A' '/ ' 

efficient  pollen  bearers 
as  winged  insects,  and 
hence  the  various  de- 
vices, such  as  hairs, 
scales,  and  constric- 
tions, at  the  throat  of 
the  corolla,  by  means 
of  which  their  access  to 
the  pollen  is  prohibited. 
To  this  class  of  adapta- 
tions belong  the  hairy 
filaments  of  the  spider- 
wort,  the  sticky  ring 
about  the  peduncles  of  weather. 

the  catchfly,  the  swollen  lips  of  the  snapdragon,  the  scales  or 
hairs  in  the  throat  of  the  hound's-tongue,  the  velvet  petals 


363 

Figs.  362,  363.  —  A  bell  flower  :    362,   position 
in  daylight ;  363,  position  at  night,  or  during  wet 


THE   FLOWER 


247 


of  the  partridge  berry,  and  the  recurved  edges  of  corollas 
like  those  of  the  morning-glory  and  tobacco,  over  which  small 
crawhng  insects  cannot  easily  climb. 

Of  flowers  that  are  pollinated  by  night  moths,  some  close 
during  the  day,  as  the  four-o'clock  and  the  evening  primrose  ; 
and  vice  versa,  the  morning-glory,  dandelion,  and  dayflower 
(Commelyna)  unfold  their  beauties  only  in  the  sunlight. 
For  similar  reasons,  night-blooming  flowers  are  generally 
white  or  very  light-colored,  and  shed  their  fragrance  only  after 
sunset.  A  nodding  position  is  assumed  by  many  flowers  at 
night,  or  during  a 
shower,  to  keep  the 
pollen  from  being  in- 
jured by  dew  or  rain- 
281.  Insect  depre- 
dators. —  The  secre- 
tion of  honey  is  a 
common  means  of 
attracting  insects, 
and  various  adapta- 
tions, such  as  spurs,  sacs,  and  pockets,  are  provided  for  pro- 
tecting it  against  unwelcome  intruders.     In  general,  plants 

that   have   long,   tubular 
'J  \     flowers,    like    the    trumpet 

honeysuckle  {Lonicera  sem- 
FiG.  365.-Headoftheswordbiii,abird   pervirens)  and  the  trumpet 

vine,    are    reserving    their 

sweets  for  humming  birds, 
or  long-tongued  moths  and  butterflies.  This  protective 
device  is  not  always  successful,  however,  against  insect  dep- 
redators, for  it  is  not  uncommon  to  find  such  corollas  with 
a  puncture  near  the  base,  made  by  wasps  or  bees,  and  some- 
times by  humming  birds  themselves,  in  their  impatience  to 
get  at  the  feast  before  the  flower  is  open.  Through  the  breach 
thus  made,  a  rabble  of  petty  thieves  can  then  find  entrance. 


Fig.  364. — A  flower  of  the  trumpet  vine  (Tecoma 
radicajis)  adapted  to  pollination  by  humnung  birds 
and  humming  bird  moths,  which  has  been  pierced  by 
a  bee  or  bird  for  honey. 


Head  of  the  swordbill,  a  l)ird 
adapted  to  feeding  on  nectar  from  long, 
tubular  corollas. 


248  PRACTICAL  COURSE  IN  BOTAxNTY 

Practical  Questions 

1.  Of  what  use  is  the  brilliant  coloring  of  the  camellia?  The  large 
flowers  of  the  magnolia  ?  The  perfume  of  the  rose  and  the  violet  ?  The 
fetid  odor  of  the  ailanthus?     (277  ;  Kxps.  81,  82.) 

2.  Are  the  tastes  of  insects  in  regard  to  odors  always  the  same  as  ours  ? 
(Exp.  82.) 

3.  Have  flowers  any  economic  value  except  for  decorative  purposes? 

4.  Can  you  name  any  that  are  used  as  food  or  beverages  ?  Any  that 
furnish  spices  and  flavorings?     Drugs,  medicines,  or  dyes? 

5.  What  commercial  food  product  is  obtained  almost  entirely  from 
flowers  ? 

6.  Name  some  of  the  flowers  that  are  most  valued  by  the  beekeeper. 

7.  Mention  another  important  industry  that  is  entirely  dependent  on 
flowers. 

8.  Name  some  of  the  flowers  that  are  most  important  to  the  per- 
fumer. 

9.  Why  do  the  seeds  of  fruit  trees  so  seldom  produce  offspring  true 
to  the  stock?     (256,257,271,277.) 

10.  Would  you  place  a  beehive  near  a  field  of  buckwheat  ?  Of  clover  ? 
Near  a  strawberry  bed  ?  In  a  peach  orchard  ?  Near  a  fig  tree  ?  Under 
a  grape  arbor? 

11.  Why  are  very  conspicuous  flowers,  like  the  camelUa,  hollyhock,  and 
pelargoniums,  so  frequently  without  odor  ? 

12.  Why  is  the  wallflower  "sweetest  by  night"?     (280.) 

13.  What  advantage  can  flowers  like  the  morning-glory  gain  by  their 
early  closing?     (280.) 

14.  Of  what  use  to  the  cotton  plant,  Japan  honeysuckle,  and  hibiscus 
is  the  change  of  color  their  blossoms  undergo  a  few  hours  after  opening? 
(277,  278,  280.) 

15.  Why  does  the  Japan  honeysuckle,  which  has  run  wild  so  abundantly 
in  many  parts  of  our  country,  produce  so  few  berries  ?     (278,  280.) 

16.  If  the  trumpet  vine  grows  in  your  neighborhood,  examine  a  number 
of  corollas  and  account  for  the  dead  ants  found  in  them.  Account  also 
for  the  large  hole  (sometimes  three  quarters  of  an  inch  in  diameter)  often 
found  near  the  base  of  the  tube.     (281.) 

17.  Do  you  see  any  connection  between  the  greater  freshness  and  beauty 
of  flowers  early  in  the  morning,  and  the  activity  of  bees,  birds,  and  butter- 
flies at  that  time  ? 

18.  The  flowers  most  frequented  by  humming  birds  are  the  trumpet 
honeysuckle,  cardinal  flower,  trumpet  vine,  horsemint  (Monarda),  wild 
columbine,  canna,  fuchsia,  etc. ;  what  inference  would  you  draw  from 
this  as  to  their  color  preferences? 


THE  FLOWER  249 

Field  Work 

1.  The  ecology  of  the  flower  is  so  suggestive  a  subject  and  so  peculiarly 
appropriate  to  outdoor  work  that  it  seems  hardly  necessary  to  point  out  the 
many  attractive  fields  of  inquiry  it  opens  to  the  student  of  nature.  In  this 
way  alone  can  experiments  in  insect  pollination  be  carried  on  to  the  best 
advantage  Try  the  effect  of  enveloping  buds  of  various  kinds  in  gauze  so 
as  to  exclude  the  visits  of  insects,  and  note  the  result  as  to  the  production 
of  fruit  and  seed.  Envelop  a  cluster  of  milkweed  blossoms  in  this  way  and 
notice  how  much  longer  the  flowers  so  protected  continue  in  bloom  than  do 
the  others ;  why  is  this  ?  Try  the  same  experiment  upon  the  blooms  of 
cotton  and  hibiscus,  if  you  live  where  they  grow,  and  see  whether  the  char- 
acteristic change  in  color  occurs  in  flowers  from  which  insects  have  been 
excluded,  and  whether  good  seed  pods  are  produced  by  them.  Try  the 
effect  upon  fruit  production  of  excluding  insects  from  clusters  of  apple, 
pear,  and  peach  blossoms. 

2.  Make  a  list  of  all  the  outdoor  plants,  both  wild  and  cultivated,  that 
are  found  blooming  in  your  neighborhood,  keeping  a  record  of  the  earliest 
specimens  of  each  as  you  find  them.  The  best  way  is  to  keep  a  sort  of 
daily  calendar,  and  at  the  end  of  each  month  give  a  summary  of  the  species 
found  in  bloom  during  that  period.  In  this  way  a  fairly  complete  annual 
record  of  the  flowering  time  of  the  different  plants  for  that  vicinity  will  be 
obtained.  The  record  should  be  kept  up  the  whole  year  round.  Don't 
stop  in  winter,  but  go  straight  on  through  the  coldest  as  well  as  the  hottest 
season,  and  you  will  make  some  surprising  discoveries,  especially  if  the 
record  is  continued  year  after  year.  Give  the  common  name  of  each  plant, 
adding  the  botanical  one  if  you  know  it.  Any  facts  that  you  may  know 
or  may  discover  in  regard  to  particular  plants,  such  as  their  medicinal  or 
other  uses,  their  poisonous  or  edible  properties,  the  insects  that  visit  them, 
and  in  the  case  of  weeds,  their  origin  and  introduction,  will  greatly  enhance 
the  interest  and  value  of  the  record. 


CHAPTER  VIII.     FRUITS 
I.    HORTICULTURAL  AND  BOTANICAL  FRUITS 

Material.  —  Green  ears  of  corn  or  wheat,  fresh  pods  of  beans,  young 
fruits  of  apple,  grape,  tomato,  melon,  buckeye,  chestnut,  or  pecan.  A 
young  fruiting  stem  of  squash,  gourd,  or  tomato. 

Appliances.  —  Coloring  fluid,  glasses  of  water,  a  piece  of  cardboard, 
tin-foil,  vaseline. 

Experiment  87.  Where  do  the  food  substances  contained  in 
FRUITS  COME  FROM  ?  —  Apply  your  food  tests  to  the  pulp  of  a  young  apple, 
squash,  bean  pod,  chestnut,  buckeye,  or  a  "green"  ear  of  corn  or  wheat, 
and  see  what  it  contains.  Te.st  the  stem  and  roots  of  a  plant  of  the  same 
kind  in  the  same  way.  Do  you  find  the  same  foods  in  them?  Where 
is  the  food  stored? 

Experiment  88.   Through  what  parts  of  the  stem  and  fruit  do 

WATER  AND  NOURISHMENT  TRAVEL  TO  THE  SEED  ?  —  Cut  a  yOUUg  Squash 

or  cucumber  from  the  vine,  leaving  stem  enough  to  insert  by  its  cut  end 
in  a  glass  of  eosin  solution.  Leave  for  two  or  three  days,  then  make  a 
vertical  section  through  the  stem  and  fruit.  What  course  has  the  liquid 
followed  ?  Can  you  trace  some  of  it  into  each  seed  ?  Do  you  see  now  a 
use  for  the  seed  stalk  and  the  rhaphe  ? 

Experiment  89.  Does  the  surface  of  fruits  give  off  water  by 
TRANSPIRATION  ?  —  Try  Exp.  39,  using  in  place  of  leaves  a  young  squash, 
eggplant,  or  a  bunch  of  grapes,  and  after  a  day  or  two  notice  whether 
any  moisture  has  been  given  off.  If  the  fruit  skin  gives  off  moisture, 
it  is  natural  to  expect  that  it  would  be  provided  with  stomata,  like  other 
transpiring  organs.  To  find  out  whether  this  is  so,  place  a  thin  piece  of 
the  outer  epidermis  of  a  grape,  tomato,  plum,  or  apple  under  the  micro- 
scope. Do  you  find  stomata  on  any  of  them  ?  Do  you  see  anything  else  ? 
Try  the  skin  of  an  apple,  and  compare  the  corky  dots  you  find  there  with 
those  on  the  bark  of  a  young  dicotyl  stem  (118)  and  decide  what  they  are. 

Experiment  90.  Will  fruits  ripen  well  in  the  absence  of  light 
AND  AIR  ?  —  Envelop  a  number  of  immature  fruits  in  bags  of  dark  cloth 
or  paper  so  that  no  light  can  reach  them.  Keep  a  number  of  others  well 
coated  with  oil  or  vaseline,  and  watch.  Do  the  fruits  so  treated  mature 
as  quickly  or  develop  as  fully  as  those  of  the  same  kind  left  untreated  ? 

250 


FRUITS 


251 


Plate  12.  —  The  inii)r<)Vfiiu'iit  of  fruits  by  cultivution  ami  scliM'tinn  :  1,  the 
common  wild  gooseberry  ;  2,  Houghton  gooseberry,  seedling  of  the  wild  form  ; 
3,  Downing  gooseberry,  seedling  of  the  Houghton.  (All  natural  size,  adapted  from 
BaUey.) 


252  PRACTICAL  COURSE   IN  BOTANY 

Experiment  91.  What  is  the  use  of  the  rind  to  the  fruit?  — 
Select  two  apples  of  equal  size,  peel  one,  and  weigh  both.  After  12  to  24 
hours,  weigh  them  again.  Which  shows  the  greater  loss  in  weight? 
Leave  peeled  and  unpeeled  fruits  in  an  exposed  place  and  see  which  is 
the  more  readily  attacked  by  insects.  Which  decays  the  sooner  ?  What 
are  some  of  the  uses  of  the  rind  ? 

282.  What  is  a  fruit  ?  —  Horticulturally  and  commercially 
the  distinction  between  a  fruit  and  a  vegetable  depends  very 
much  upon  the  use  we  make  of  it  —  whether  as  food,  or  as  a 
mere  gratification  of  the  palate.  Broadly  speaking,  those 
fruits  that  are  lacking  in  sugar,  as  the  tomato  and  cucum- 
ber, are  classed  as  vegetables.  Botanically,  a  fruit  is  any 
ripened  seed  vessel,  or  ovary,  with  such  connected  parts  as 
may  have  become  incorporated  with  it ;  and  hence,  to  the 
botanist,  a  boll  of  cotton,  a  tickseed,  or  a  cocklebur  is  just 
as  much  a  fruit  as  a  peach  or  a  watermelon, 

283.  Classification  of  fruits.  —  For  convenience  of  de- 
scription, fruits  are  classed  as : 

(a)  Dry  or  fleshy,  according  as  they  have  a  more  or  less 
hard  and  bony,  or  soft  and  fleshy,  texture. 

(b)  Dehiscent,  or  indehiscent,  according  as  they  open  at 
maturity  in  a  regular  way  to  discharge  their  seed,  or  remain 
closed  until  the  covering  wears  away  or  is  burst  by  the  germi- 
nating embryo. 

Fleshy  fruits  are  very  seldom  dehiscent,  though  some  few, 
as  the  balsam  apple  and  the  chayote,  or  one-seeded  squash, 
discharge  their  seed  when  mature.  The  banana  and  some 
other  fleshy  fruits,  when  peeled,  separate  along  regular  lines, 
and  in  this  respect  behave  very  much  as  if  they  were  fleshy 
pods. 

284.  When  is  a  fruit  ripe  ?  —  A  fruit  is  ripe  horticulturally, 
when  it  is  good  to  eat ;  it  is  ripe  botanically,  when  it  has  set 
its  seed.  Many  of  our  choicest  table  fruits,  such  as  the  pine- 
apple, banana,  and  most  varieties  of  fig,  seldom  are  botani- 
cally ripe,  since  they  rarely  produce  perfect  seeds. 

It  is  the  constant  effort  of  the  horticulturist  to  develop 


FRUITS 


253 


those  parts  of  a  plant  that  are  useful  to  man,  while  in  a  state 
of  nature  the  plant  seeks  to  develop  such  parts  as  best  serve 
its  own  purpose  in  the  struggle  for  existence.  The  plants 
most  useful  to  man  have,  as  a  general  thing,  been  subjected 
to  a  long  course  of  artificial  breeding  and  selection.  They 
are  forced  developments,  often  monstrosities,  from  the  plant's 
point  of  view,  if  we  could  conceive  of  it  as  capable  of  having 
an  opinion.  Nature  is  continually  striving  to  reclaim  them; 
and  if  left  to  themselves,  they  must 
either  obey  "  the  call  of  the  wild," 
or  die  out. 

285.  Seedless  fruits  and  vegeta- 
bles. —  As  the  seed  is  the  most 
important  thing  to  the  plant,  the 
edible  parts  in  wild  fruits  are,  as  a 
rule,  subsidiary  to  its  development. 
In  a  state  of  nature,  fruits  will  gen- 
erally wither  and  drop  from  the 
stem,  if  for  any  reason  they  have 
become  incapable  of  perfecting  their 
seed.  It  is  only  in  a  few  kinds,  limited  to  those  which  can 
successfully  propagate  themselves  by  other  means,  that  the 
production  of  seed  does  not  take  place.  Among  cultivated 
species,  however,  where  propagation  is  carefully  provided 
for  by  man,  the  seed  is  of  less  importance,  and  sterile  vari- 
eties that  might  soon  die  out  under  natural  conditions,  con- 
tinue their  existence  indefinitely  under  his  fostering  hand. 
The  seeds  of  edible  fruits  are,  as  a  general  thing,  both  indi- 
gestible and  unpalatable  (21),  and  hence  the  efforts  of  the 
horticulturist  are  directed  largely  to  getting  rid  of  them,  or 
to  very  greatly  reducing  their  size  and  number  in  proportion 
to  the  edible  parts. 

286.  How  seedless  fruits  arise.  —  The  perfecting  of  seed 
requires  a  great  consumption  of  food  and  energy  on  the  part 
of  the  plant,  and  when  it  is  led,  for  any  reason,  to  expend 
an  unusual  amount  of  force  in  some  other  function,  —  as 


Fig.  366.  — a  seedless  cit- 
range,  hybrid  between  the  or- 
ange and  the  lemon. 


254         PRACTICAL  COURSE  IN  BOTANY 

for  instance,  in  producing  tubers  or  in  growing  bulbs,  — 
it  is  apt  to  bear  few  seeds  and  to  depend  more  or  less  com- 
pletel}'  upon  other  methods  of  reproduction. 

Among  cultivated  plants,  selection  on  the  part  of  man, 
whether  conscious  or  unconscious,  has  perhaps  contributed 
more  than  any  other  cause  to  bring  about  the  same  result. 
To  this  agency  is  probably  due  the  development  of  our  com- 
mon domestic  fig,  of  which  over  four  hundred  varieties  that 
mature  fruits  without  fertilization  are  cultivated  in  the  United 
States  alone.  The  fig  was  one  of  the  earliest  fruits  known  to 
cultivation;  and  the  early  navigators,  ignorant  of  the  processes 
of  fertilization,  would  naturally,  in  choosing  specimens  to 
carry  home  with  them,  select  only  fruit-bearing  trees.  Such 
of  these  as  matured  fruits  would  be  preserved  and  propagated, 
until,  by  repeated  selection,  hundreds  of  edible  varieties  have 
been  developed  that  ripen  fruits  without  caprification  (279) . 

287.  The  use  of  the  fruit  to  the  plant.  —  The  object  of 
the  fruit  is  to  furnish  protection  to  the  seeds  during  their 
period  of  development  and  inactivity,  and  to  aid  in  various 
ways  the  work  of  dispersal.  It  probably  takes  part  also  in 
digesting  and  diffusing  nourishment  for  the  use  of  the  develop- 
ing seeds.  It  has  been  shown  in  previous  chapters  that  plants, 
almost  without  exception,  are  in  the  habit  of  storing  up 
food  in  various  ways  as  a  provision  for  fruiting.  That  a 
large  portion  of  the  stored  nourishment  is  used  up  in  the  per- 
formance of  this  function  is  proved  by  its  disappearance  from 
those  parts  —  for  example,  from  fleshy  roots,  such  as  beets 
and  turnips,  after  they  have  "  gone  to  seed." 

Practical  Questions 

1 .  What  is  the  use  of  the  down  on  the  peach  ?  The  bloom  of  the  plum 
and  grape?     [202,  (1);  Exp.  91.] 

2.  Why  are  apples,  pears,  plums,  and  other  fleshy  fruits  nearly  always 
rosier  on  one  side  than  on  the  other?     (Exp.  90.) 

3.  Can  annuals  be  improved  in  any  other  waj^  than  by  seed  selec- 
tion? 

4.  Would  a  seedless  annual  be  perpetuated  under  natural  conditions  ? 


FRUITS 


255 


5.  Why  is  decrease  of  moisture  and  increase  of  light  desirable  as  the 
fruiting  season  approaches?     (126,  127;  Exp.  90.) 

6.  Why  are  turnips,  carrots,  and  other  fleshy  roots  unfit  to  eat  if  left 
over  till  the  plants  have  seeded  ?     (92,  287.) 


II.     FLESHY    FRUITS 

Material.  —  A  specimen  of  each  of  the  four  principal  kinds  of  fleshy 
fruits.  Examples  of  the  pome  are  :  apple,  pear,  quince,  rose  hip,  haw ;  of 
the  berry :  grape,  tomato,  cranberry,  currant,  gooseberry,  lemon ;  of  the 
pepo  :  melon,  squash,  pumpkin ;  of  the  drupe  :  peach,  plum,  cherry,  dog- 
wood. Specimens  of  the  commoner  kinds  can  nearly  always  be  found  in 
the  market ;  if  nothing  better  is  available,  pickled  and  dried  ones  may  be 
used  —  figs,  prunes,  dates,  raisins,  etc. 


—  Examine  with  a  lens 
Can  you  make  out  the 


288.  Dissection  of  a  pome  fruit. 

the  outside  of  an  apple  or  a  pear, 
lenticels  ?  What  difference 
in  color  do  you  notice  be- 
tween the  ripe  and  unripe 
fruit?  What  difference  in 
taste?  What  substance 
would  you  judge  from  this, 
do  ripe  fruits  contain 
which  green  ones  do  not? 
Test  both  kinds  for  sugar 
and  starch  ;  which  contains 
the  more  of  each?  Strictly 
speaking,  sugar  and  starch 
are  merely  different  forms 
of  the  same  chemical  compound.  In  ripe  fruits  the  starch 
has  been  cooked  by  the  sun  and  converted  into  sugar. 

With  the  point  of  a  pencil  separate  the  little  dry  scales  that 
cover  the  depression  in  the  center  of  the  fruit  at  the  end  oppo- 
site the  stem.  How  many  of  them  arc  there  ?  How  does  this 
accord  with  the  plan  of  the  flower  as  outlined  in  229  ?  They 
are  the  remains  of  the  sepals,  as  will  be  more  apparent  on 
comparing  them  with  the  larger  and  more  leaf  like  ones  on 
a  hip,  which  is  clearly  only  the  end  of  the  footstalk  enlarged 


tj( .  —  Outside  of  an  apple,  show- 
ing lenticels  on  the  skin. 


256 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  308. — Cross  section 
of  a  pome  :  ;)/,  placenta  ;  c, 
carpels  ;  /,  fibrovascular  bun- 
dles. 


and  hollowed  out  with  the  caljrx  sepals  at  the  top.  Cut  a 
cross  section  midway  between  the  stem  and  the  blossom  end, 
and  make  an  enlarged  sketch  of  it.  Label  the  thin,  papery 
walls  that  inclose  the  seed,  carpels. 
How  many  of  them  are  there,  and  how 
many  seeds  does  each  contain  ?  The 
carpels,  together  with  all  that  portion 
of  the  fruit  which  surrounds  and  ad- 
heres to  the  ovary,  constitute  the  peri- 
carp, or  wall  of  the  seed  vessel.  The 
fleshy  part  of  the  apple  is  no  part  of 
the  ovary  proper,  but  consists  merely 
of  the  receptacle,  or  end  of  the  foot- 
stalk, which  becomes  greatly  enlarged 
and  thickened  in  fruit.  Look  for  a 
ring  of  dots  outside  the  carpels,  connected  (usually)  by  a 
faint  scalloped  line.  How  many  of  these  dots  are  there  ?  How 
do  they  compare  in  number  with  the  carpels  ?  With  the  rem- 
nants of  the  sepals  adhering  to  the  blossom  end  of  the  fruit  ? 

Next  make  a  vertical  section 
through  a  fruit,  and  sketch,  enlarg- 
ing it  sufficiently  to  show  all  the 
parts  distinctly.  Observe  the  line  of 
woody  fibers  outside  the  carpels,  in- 
closing the  core  of  the  apple.  Com- 
pare this  with  your  cross  section  ;  to 
what  does  it  correspond  ?  Where  do 
these  threads  originate?  Where  do 
they  end  ?  Can  you  make  out  what 
they  are?  (176.)  Notice  how  and 
where  the  stem  is  attached  to  the 
fruit.     Label  the  external  portion  of 

the  stem,  peduncle ;  the  upper  part,  from  which  the  fibrovas- 
cular bundles  branch,  the  receptacle.  It  is  the  enlargement 
of  this  which  forms  the  fleshy  part  of  the  fruit.  Try  to  find 
out,  with  the  aid  of  your  lens  and  dissecting  pins,  the  exact 


Fig.  369.  —  Vertical  section 
of  a  pome :  p,  peduncle ;  /, 
fibrovascular  bundles ;  s,  seeds ; 
pi,  placenta  ;  c,  carpel. 


FRUITS 


257 


spot  at  which  the  seeds  are  attached  to  the  carpels,  and 
label  this  point,  placenta.  Notice  whether  it  is  in  the  axis 
where  the  carpels  all  meet  at  their  inner  edges,  or  on  the 
outer  side.  Observe,  also,  whether  the  seed  is  attached  to 
the  placenta  by  its  big  or  its  little  end.  If  you  can  find  a 
tiny  thread  that  attaches  the  seed  to  the  carpel;  label  it,  seed 
stalk.  Fruits  of  this  kind  are  classed,  botanically,  as  pomes. 
Write,  from  your  analysis,  a  definition  of  the  pome. 

289,  Modifications  of  the  receptacle.  —  Compare  with  the 
drawings  you  have  made,  a  haw  and  a  hip.  What  points  of 
agreement  do  you  see  ?  What  dif- 
ferences ?  Which  of  the  two  more 
closely  resembles  the  typical  pome  ? 
The  receptacle  is  subject  to  a  va- 
riety of  modifications,  and  forms  a 
part  of  many  fruits,  for  example, 
the  fig,  lotus,  and  calycanthus 
(Figs.  370,  371) ;  but  a  fruit  is  not 
a  pome  unless  the  containing  re- 
ceptacle becomes  more  or  less  soft 
and  edible. 

290.  The  pepo,  or  melon.  —  Next 
examine  a  gourd,  cucumber,  squash, 
or  any  kind  of  melon,  and  compare  its  blossom  end  with  that 
of  the  apple  or  pear.  Do  you  find  any  remains  of  a  calyx, 
or  other  part  of  the  flower  ?  Examine  the  peduncle  and  ob- 
serve how  the  fruit  is  attached  to  it.  Can  you  tell  what 
made  the  outer  epidermis  of  the  rind?  Put  a  small  piece 
under  the  microscope  ;  do  you  see  any  stomata,  or  lenticels  ? 
Cut  cross  and  vertical  sections,  and  sketch  them,  labeling 
each  part.  There  may  be  some  difficulty  in  making  out  the 
carpels,  for  they  are  not  separate  and  distinct  as  in  the  pome, 
but  confluent  with  the  enlarged  receptacle,  which  in  these 
fruits  forms  the  outer  portion  of  the  rind,  and  also  with  each 
other  at  their  edges,  so  as  to  form  one  unbroken  circle,  as  if 
they  had  all  grown  together.     And  this  is  precisely  what 


370 


Fk 


371 
370,    371.  —  Enlarged 


receptacle  of  Carolina  allspice 
{Calycanthus),  containing  fruits 
attached  to  its  inner  surface : 
370,  exterior ;  371,  vertical  sec- 
tion. 


258 


PRACTICAL  COURSE  IN  BOTANY 


Fi<i.  ;i 7 2.  — Cross 
section  of  gourd  :  c,  one 
of  the  carpels  in  dia- 
gram.   {After  Gray.) 


has  happened.  The  placentas  are  greatly  enlarged  and 
modified,  and  it  may  be  necessary  to  refer  to  the  diagram, 
Fig.  372,  c,  in  order  to  make  them  out.  How  many  locules, 
or  chambers,  are  there  in  your  specimen?  How  many 
placentas?  Notice  that  these  are  central 
and  double,  but  extend  to  the  pericarp  be- 
fore dividing  so  that  they  appear  to  be  pa- 
rietal, and  twice  their  real  number,  which 
is  only  three.  Are  the  seeds  vertical,  as  in 
the  apple,  or  horizontal?  Look  for  the 
little  stalk,  or  thread,  that  attaches  them 
to  the  placenta. 

Pepo  is  the  name  given  by  botanists  to 
this  kind  of  fruit.     Write  in  your  notebook 
a  proper  definition  of  it,  from  the  specimens  examined. 

291.  The  berry.  —  Examine  a  tomato,  an  eggplant,  a 
grape,  cranberry,  lemon,  or  orange,  in  both  cross  and  ver- 
tical section,  and  compare  it  with  the  melon  and  the  apple. 
What  differences  and  resemblances  do  you  find?  Cut  a 
cross  section,  and  draw,  showing  the  attachment  of  the  seeds. 
How  many  locules  are  there?  Normally  the  tomato  is  a 
two-celled  fruit,  like  the  potato  berry  (Fig.  374),  but  it  has 
been  so  modified  by  cultivation  that 
the  original  plan  is  not  always  easy 
to  distinguish.  See  if  you  can  make 
it  out.  Do  the  seeds  in  your  speci- 
men appear  to  be  healthy  and  well 
developed,  or  are  some  of  them  small 
and  aborted  ?  How  do  you  account 
for  this?  (285,286.)  What  differ- 
ence do  you  notice  in  color  between 
the  ripe  and  unripe  fruit?  Write  a 
definition  of  the  berry  from  the  study  you  have  made  of  it. 

Berries  are  the  commonest  of  all  fleshy  fruits,  and  the  most 
variable  and  difficult  to  define.  In  general,  any  soft,  pulpy, 
or  juicy  mass,  like  the  grape  and  tomato,  whether  one  or 


Figs.  373,  374.  —  A  potato 
berry  :  373,  exterior  ;  374,  cross 
section. 


FRUITS  259 

many  seeded,  inclosed  in  a  containing  envelope,  whether 
skin  or  rind,  is  a  berry.  Its  typical  forms  are  such  fruits  as 
the  grape,  mistletoe,  pokeberry,  etc.,  though  such  diverse 
forms  as  the  eggplant,  persimmon,  red  pepper,  orange,  ba- 
nana, and  pomegranate  have  been  classed  as  berries;  and, 
in  fact,  the  melon  and  the  pumpkin  are  only  greatly  modified 
kinds  of  the  same  fruit.  In  popular  language,  any  small, 
round,  edible  fruit  is  called  a  berry.  This  is  a  good  commer- 
cial classification,  though  not  botanically  correct. 

292.  The  drupe,  or  stone  fruit.  — ■  Examine  a  section  of  a 
green  plum,  peach,  or  cherry,  before  the  stone  has  hardened, 
and  tell  from  what  part  it  is  formed.  This  stony  covering, 
composed  of  the  inner  layer  of  the  pericarp,  and  enveloping 
the  seed  like  an  outer  coat,  is  the  main  dis- 
tinction between  the  drupe  and  the  berry, 
but  it  is  not  always  possible  to  make  out  its 
real  nature  except  by  an  examination  of  the 
young  ovary.  In  a  green  drupe,  before  the 
stone  has  hardened,  its  connection  with  the  ^.  ^'^"  '^.'^^'""y'"" 

'   ^  ^  _       tical    section    of    a 

fleshy  part  is  very  evident,  and  the  ripe  fruit  drupe.  {After 
will  answer  inquiries  if  w^e  know  how  to  put 
them.  Open  the  stone,  and  the  seed  will  be  exposed  with  its 
own  coverings  inside.  When  a  stone  has  more  than  one 
kernel,  —  for  instance,  an  almond  or  peach  stone,  ■ —  the 
stone  is  not  a  seed  coat,  but  the  hardened  inner  wall  of  a 
seed  vessel  or  ovary ;  for  a  seed  coat  can  never  contain  more 
than  one  seed,  any  more  than  the  same  skin  can  contain 
more  than  one  animal. 

All  the  fruits  considered  in  this  section  belong  to  the  fleshy 
class.  These  form  the  bulk  of  the  fruits  sold  in  the  market, 
and  are  of  special  importance  to  the  horticultmist. 

Practical  Questions 

1.  Is  the  tomato  liorfunilturally  a  fruit  or  a  vegetable?  the  squash? 
eggplant?  craiiherry ?  olive?  elderberry?  pepper?  date?  maypop?  crab 
apple?   black  haw?    To  what  glass  does  e;^ch  belong?     (283,  2S8-292.) 


260  PRACTICAL  COURSE   IN  BOTANY 

2.  Of  what  use  to  the  plant  is  the  hard  stone  of  the  drupe?     (21.) 

3.  Is  the  pulp  of  fleshy  fruits  agreeable  to  the  taste  before  they  are 
ripe?    After?     What  advantage  is  this  to  the  plant ?     (21.) 

4.  Are  the  seeds  of  edible  fruits,  as  a  general  thing,  digestible  or  agree- 
able to  the  palate  ? 

5.  Is  this  an  advantage  to  man?    To  the  plant?     (21,  284,  285.) 

6.  What  are  the  most  common  fleshy  fruits  in  autumn  ? 

7.  With  what  vegetative  parts  of  the  plant  does  the  skin  of  many 
fruits  present  correspondences  ?  Are  these  such  as  to  indicate  homology, 
or  analogy  only,  between  them?     (100,  118,  288,  289;  Exp.  89.) 

8.  Name  six  of  the  most  watery  fruits  that  grow  in  your  neighborhood. 

9.  Under  what  conditions  as  to  soil,  heat,  moisture,  etc.,  does  each 
thrive  best  ? 

10.  Would  a  gardener  act  wisely  to  infer  that  because  a  fruit  contains 
a  great  deal  of  water  it  should  be  planted  in  a  very  wet  place  ? 

11.  Which  contains  more  water,  the  fruit  or  the  leaves  of  the  apple  ? 

12.  Why  does  not  the  fruit,  when  separated  from  the  tree,  wither  as 
quickly  as  do  the  leaves?     (Exp.  91.) 

III.     DRY  FRUITS 

Material.  —  Some  easily  attainable  specimens  of  dry  fruits  are  (1)  nuts: 
acorn,  hickory  nut,  walnut,  chestnut,  pecan,  filbert ;  (2)  pods  :  pea  and  bean 
pods,  capsules  of  larkspur,  milkweed,  jimson  weed,  cotton ;  (3)  grains  :  corn, 
wheat,  oats,  rice;  (4)  akene:  sunflower,  thistle,  dandelion,  buckwheat, 
clematis. 

293.  Importance  of  dry  fruits.  —  Dry  fruits  are  not  in 
general  so  conspicuous  or  so  attractive  as  fleshy  ones,  but  on 
account  of  their  great  number  and  variety  they  offer  a 
wide  field  for  study.  They  are  also  of  great  interest  from  an 
economic  point  of  view:  (1)  because  they  include  the  cereal 
grains  that  furnish  so  large  a  portion  of  our  food,  and  (2) 
because  the  greater  part  of  the  troublesome  weeds  that  infest 
our  crops  are  scattered  by  fruits  of  this  class. 

294.  Indehiscent  fruits.  —  These  kinds  are  so  simple  that 
it  will  not  be  necessary  to  give  much  time  to  them.  Compare 
an  acorn,  a  chestnut,  or  a  filbert  with  a  ripe  bean  pod  or  with 
a  capsule  of  morning-glory.  Try  to  open  each  with  your 
fingers ;  which  dehisces,  or  opens,  the  more  readily  ?  Which  is 
indehiscent,  having  no  regular  way  of  opening  ?     How  many 


FRUITS 


261 


seeds  or  kernels  do  you  find  in  the  dehiscent  pod?  How 
many  in  the  indehiscent  one?  Would  it  be  of  any  advan- 
tage for  a  one-seeded  pod  to  open?  Remove  the  kernel 
from  the  indehiscent  fruit ;  has  it  any  covering  besides  the 
shell  ?     Which  is  the  pericarp,  and  which  the  seed  coat  ? 

295.  The  nut  is  easily  recognized  by  its  hard,  bony  cover- 
ing, containing  usually,  when  mature,  a  single  large  seed  that 
fills  the  interior.  Care  should  be  taken  not  to  confound  with 
true  nuts,  large  bony  seeds,  like  those  of  the  buckeye,  horse- 


376  377 

Figs.  376,  377.  —  Nut  of  the  pecan 
tree  :  376,  exterior  ;  377,  cross  section. 


Figs.  378,  379.  — Nutlike  seeds: 
378,  horse-chestnut ;  379,  seed  of  the 
fetid  sterculia. 


chestnut,  date,  and  the  Brazil  nut  sold  in  the  markets.  In 
the  true  nut,  the  hard  covering  is  the  seed  vessel,  or  pericarp, 
and  not  a  part  of  the  seed  itself,  though  it  often  adheres  to  it 
so  closely  as  to  seem  so.  In  bony  seeds,  like  those  of  the  horse- 
chestnut  and  persimmon,  the  hard  covering  is  the  outer  seed 
coat.  The  distinction  is  not  always  easy  to  make  out  unless 
the  seed  can  be  examined  while  still  attached  to  the  placenta 
of  the  fruit. 

296.  The  akene,  of  which  we  have 
examples  in  the  tailed  fruit  of  the 
clematis,  the  tiny  pits  on  the  straw- 
berry, and  the  so-called  seeds  of  the 
thistle,  dandelion,  and  sunflower,  is  a 
small,  dry,  one-seeded,  indehiscent 
fruit,  so  like  a  naked  seed  that  it  is 
generally  taken  for  one  by  persons  not 
acquainted  with   botany.     It  is  the 


380 


3S1 


Figs.  380,  381.  — Akcnes 
(magnified)  :  3S0,  of  buck- 
wheat ;  381,  of  cinquefoil. 


262 


PRACTICAL  COURSE  IN  BOTANY 


.383 


384 


Figs.  382-384.  — Cremocarps,  fruits  of 
the  parsley  family. 


commonest  of  all  fruits,  and  there  are  so  many  kinds  that 
special  names  have  been  applied  to  some  of  the  most  marked 

varieties.  The  akene  of  the 
composite  family  may  gen- 
erally be  known  by  the 
various  appendages  in  the 
form  of  scales,  hooks,  hairs, 
or  chaff,  that  crown  it  (Figs. 
309-314).  The  fruits  of  the 
parsley  family  are  merely  a 
sort  of  double  akene  at- 
tached by  the  inner  face 
to  a  slender  stalk  from  which  it  separates  at  maturity. 
The  samara,  or  key  fruit,  is  an  akene  provided  with  a 
wing  to  aid  in  its  disper- 
sion by  the  wind.  The  l^^ 
maple,  ash,  and  elm  fur- 
nish familiar  examples. 

297.  The  grain,  so  fa- 
miliar to  us  in  all  kinds  of 
grasses,  is  economically 
the  most  important  of  all 
fruits.  It  is  popularly 
classed  as  a  seed,  and  for  practical  purposes  may  be  treated 
as  such,  but  it  is  really  a  modification  of  the  akene  in  which 
the  seed  coats  have  so  completely  fused  with  the  pericarp 
that  they  can  no  longer  be  distinguished 
as  separate  organs.  Peel  the  husk  from 
a  grain  of  corn  that  has  been  soaked  for 
twenty-four  hours,  and  you  will  find  the 
contents  exposed  without  any  covering ; 
remove  the  shell  of  an  acorn  or  a  hickory 
nut,  and  the  seed  will  still  be  enveloped 
by  its  own  coats.  Would  it  be  of  any 
advantage  for  the  seed  of  an  indehiscent  fruit,  like  a  grain  of 
corn  or  oats,  to  have  a  separate  special  covering  of  its  own  ? 


385 
Figs.  385,  38G. 


386 

—  Samaras  :  385,  ailanthus  ; 
38G,  maple. 


387 

Figs.  387,  388.  —  Grain 
of  wheat  with  husks  on : 
387,  front  view  ;  388,  back 
view. 


FRUITS 


263 


Fig.  389.  —  Follicle 
of  milkweed. 


Fig.  390.  — Leaf- 
like follicle  of  Japan 
varnish  tree :  S, 
outer(dorsal)  suture  ; 
S',  inner  (ventral) 
suture. 


298.  Dehiscent  fruits.  —  Pod,  or  capsule,  is  the  general 
name  applied  to  all  dehiscent  fruits.  The  simplest  possible 
kind  of  pod  is   the  follicle,  composed  of  a 

single  carpel,  like  those  of 
the  larkspur,  milkweed,  and 
marsh  marigold,  and  may  be 
regarded  as  a  modified  leaf. 
Examine  one  of  these  pods 
and  you  will  find  that  it 
splits  down  one  side,  which 
corresponds  to  the  edges  of 
the  leaf  brought  together 
and  turned  inward  to  form 
a  placenta  for  the  attach- 
ment of  the  seed.  This  line 
of  union  is  called  a  "su- 
ture," from  a  Latin  word 
meaning  a  "seam." 

299.  The  legume.  —  Get  a  pod  of  any  kind  of  bean  or 
pea,  and  observe  that  it  differs 
from  the  follicle  in  having  two 
sutures  or  lines  of  dehiscence. 
One  of  these  runs  along  the  back 
of  the  carpel  and  corresponds 
to  the  midrib  of  the  leaf;  the 
other,  corresponding  to  the 
united  edges  of  the  carpellary 
leaf,  always  turns  inward, 
toward  the  axis  of  the  flower, 
and  forms  the  placenta. 

The  beggar-ticks,  so  unpleas- 
antly familiar  to  most  of  us, 
are  merely  a  kind  of  legume  con- 
stricted between  the  seeds  and 

breaking  up  into  separate  joints  ff^^^^  ^^  ^  ^^^  ^ith  partially  con- 
at    maturity.     What    kind    of 


391 

Figs.   391-393. 
legume   of    bean  : 
d,    dorsal    suture  ; 


392  393 

—  Legumes:  391, 
,  ventral  suture  ; 
392,    constricted 


legume  of  senna  (CassiaNelsonia);  393, 
legume  of   a 
Btricted  pod. 


264 


PRACTICAL  COURSE  IN  BOTANY 


indehiscent  fruits  do  the  joints  become 
when  separated  ?     (296.) 
300.   Compound  or  syncarpous  pods. 


Fig.  394.  —  Loment  of 
beggar-ticks. 

—  The  carpellary  leaves  may 
unite  either  by  their  open 
edges,  as  if  a  whorl  like  that 
represented  in  Fig.  188  were 
to    grow    together    by    the    capsule  of  frost- 

/■n-        orvr\  1       weed,  with  parie- 

margms  {r  ig.  395) ;  or  each 


Fio.  395.  — Cross 
section  of  one- 
celled  syncarpous 


Fig.  396.  — Folli- 
cles of  larkspur 
borne  on  the  same 
torus,  but  dis- 
tinct. 


tal    place ntae. 

may  first  roll  itself  into  a    (^/'«''  ^"^^-^ 
shnple  follicle  like  the  lark- 
spur and   columbine    (Fig.  396),   and   then  a  number  of 
these  may  unite  by  their  ventral  sutures  into  a  single  syn- 
carpous capsule,  with  as  many  locules  as  there  are  carpels 


397 

Fig.  397.  — Pods  of 
Echeveria,  contig- 
uous, but  distinct. 


398 

Fig.  398.  —  Capsule  of 
Colchicum,  with  carpels 
united  into  a  syncarpous 
pod. 


399 

Fig.  399.  —  Capsule 
of  corn  cockle,  with 
free  central  placenta. 


(Fig.  398).  The  seed-bearing  sutures  being  all  brought  to- 
gether in  the  center,  the  placenta  becomes  central  and  axial. 
In  the  first  case  (Fig.  395)  the  open  carpels  form  a  one- 
chambered  capsule,  though  the  placentas  sometimes  project, 
as  in  the  cotton,  so  far  as  to  produce  the  effect  of  true 
partitions  with  a  central  axial  placenta.     In  capsules  with 


FRUITS  265 

only  one  compartment,  the  number  of  carpels  can  generally 
be  determined  by  the  number  of  sutures  or  of  placentas. 

Practical  Questions 

1.  To  what  class  of  fruits  does  each  of  the  following  belong  —  rice; 
beggar-ticks;   poppy;    peanut;   jimsonweed;    chinquapin;    caraway? 

2.  Is  the  coconut,  as  usually  sold  in  the  market,  a  fruit  or  a 
seed? 

Suggestion :  carefully  examine  the  "  eyes,"  from  without  and  from 
within;  if  you  can  get  a  specimen  with  the  husk  on,  it  will  help  to  a 
decision. 

3.  Can  you  name  any  syncarpous,  or  compound  capsule,  that  is  single- 
seeded  ? 

4.  Can  you  name  any  indehiscent  fruit  that  has  normally  more  than 
one  seed  ? 

5.  Give  a  reason  for  the  difference.     (23.) 

6.  Name  the  weeds  of  your  neighborhood  that  are  most  troublesome 
on  account  of  their  adhesive  fruits. 

7.  Do  these  fruits  belong,  as  a  rule,  to  the  dehiscent  or  to  the  indehis- 
cent class  ? 

8.  Give  a  reason  for  the  difference,  if  any  is  noted.     (23.) 


IV.    ACCESSORY,    AGGREGATE,    AND    MULTIPLE    FRUITS 

Material.  —  For  autumn  and  winter,  examples  of  accessory  fruits 
are :  pineapple,  common  apple,  pear,  rose  hip ;  aggregate :  magnolia, 
tulip  tree,  wild  cucumber,  sweet  flag  (Calamus) ;  multiple :  osage  orange, 
sweet  gum  balls,  pine  cones,  figs,  fresh  or  dried. 

For  spring  and  summer,  examples  of  accessory  fruits  are :  raspberry, 
strawberry,  squash,  cucumber ;  aggregate :  strawberry,  blackberry,  Jack- 
in-the-pulpit ;  multiple :  fig,  mulberry.  Most  of  those  named  ^^^ll  be 
found  to  belong  to  more  than  one  class ;  the  strawberry,  for  instance,  is 
both  accessory  and  aggregate;  the  fig  and  pineapple,  accessory  and 
multiple. 

301.  Besides  the  varieties  already  named,  all  fruits, 
whether  fleshy  or  dry,  may  be  simple,  accessory,  aggre- 
gate, or  collective.  Fruits  of  the  first  kind  need  no  ex- 
planation;   they  consist  merely  of  a  single  ripened  ovary, 


266        PRACTICAL  COURSE  IN  BOTANY 

whether  of  one  or  more  carpels,  as  the  peach,  cherry,  bean, 
and  lemon. 

302.  Accessory  fruits  are  so  called,  because  some  other 
part  than  the  seed  vessel,  or  ovary  proper,  is  coherent  with, 
or  accessory  to  it,  in  forming  the  fruit,  as  in  the  apple  and 
the  hip.  The  accessory  part  may  consist  of  any  organ,  but 
is  more  frequently  the  calyx  or  the  receptacle.  In  the  straw- 
berry, the  little  hard  bodies,  usually  called  seeds,  that  dot 
the  surface  are  the  true  fruits  (akenes).  A  vertical  section 
through   the    center  will   show  the  edible  part  to  consist 


400  401 

FiQS.  400,  401. — Vertical  sections  showing  the  relation  between  a  strawberry 
flower  and  fruit:  400,  the  flower;  401,  the  fruit  developed  from  it.  The  corre- 
sponding parts  are  indicated  by  connecting  lines  ;  r,  receptacle  ;  a,  sepal ;  b,  petal ; 
8,  stamens  ;  c,  carpel  (akene  in  fruit)  ;  p,  style  of  the  pistil ;  pi,  pulp  of  the  fruit. 

wholly  of  the  enlarged  receptacle.  In  the  pineapple,  the 
edibla  stalk  may  be  traced  through  a  mass  of  flowers 
whose  seed  vessels  have  become  enlarged  and  ripened  into 
fruits. 

303.  Aggregate  fruits.  —  Some  accessory  fruits,  the  straw- 
berry and  blackberry  for  example,  are,  at  the  same  time, 
aggregate  ;  that  is,  they  are  composed  of  a  number  of  sepa- 
rate individual  fruits  produced  from  a  single  flower.  The 
cone  of  the  magnolia  and  of  the  tulip  tree  are  aggregate 
fruits;  can  you  name  any  others? 


FRUITS 


267 


304.  Collective,  or  multiple,  fruits.  —  The  pineapple  is  an 
example  of  both  an  accessory  and  a  multiple  fruit,  being 
composed  of  the 
ripened  ovaries  of  .  v  N.  A- 
a  number  of  sep- 
arate flowers  that 
have  become 
more  or  less  co- 
herent. Theosage 
orange,  sweet 
gum  balls,  fig,  and 
mulberry  are 
other  examples 
of  this  class. 

305.  Dissection 
of  a  multiple  fruit. 
—  Get  one  of  the 
dried  figs  sold  by 
the  grocers.  Look 
at  the  small  end      ^       ._„  ._.      ,.  „•  ,    r    .    r  .u 

Figs.  402-404.  —  Multiple  fruit  of  the  pineapple : 
where  the  skin  402,  external  vaew  of  a  ripe  fruit,  showing  the  prolonged 
nricririQfps-  nf  wViQf  receptacle  growing  into  a  new  plant  above,  and  the  scaly 
UligiXld;ieb,  Ul  Wllctt  bracted  covering  below  ;  40.3,  vertical  section  through  the 
part  is  it  a  modi-  ^xls  of  a  fruit,  showing  a,  the  receptacle,  with  6,  b,  the 
fi  ,•  f)  r  OQCi  \  ^*'*'^y  ovaries  cohering  around  it  and  forming  the  edible 
ncailOn  .  (^  Z  O  v.)  p^rt  of  the  fruit ;  404,  a  single  "  eye  "  or  scale,  somewhat 
Can  VOU  think  of  reduced,  showing  the  scaly  bract  from  the  axil  of  which 
the  (generally)  abortive  flower  originates. 

a  reason  for  this 

curious,  urnlike  enlargement  of  the  receptacle  ?  Is  there  any- 
thing about  the  fig,  for  instance,  that  renders  it  peculiarly 
liable  to  be  preyed  upon  by  birds  and  insects  ?  Could  any 
but  a  very  small  insect  get  through  the  eye  without  in- 
juring the  fruit?  Could  it  free  itself  from  the  sticky  mass 
inside  and  get  out  again  without  difficulty?  Would  you 
judge  from  this  that  the  caprification  of  the  fig  is  easily 
effected  (279),  even  when  the  fig  wasp  is  present?  Can  you 
now  account  for  the  fact  that  over  four  hundred  varieties  of 
cultivated  figs  ripen  their  fruit  without  fertilization  ? 


402 


40.3 


2G8 


PRACTICAL  COURSE   IN  BOTANY 


Open  your  specimen  and  examine  the  contents ;  what  do 
you  find  ?  From  a  dried  specimen  it  will  hardly  be  practicable 
to  make  out  clearly  that  the  pulp  of  the  fig  consists  of  hun- 
dreds of  tiny  pistillate  blossoms  that  line  the  inner  face  of  the 
receptacle.  The  little  grains  usually 
taken  for  seeds  are  really  small  akenes 
—  the  ripened  ovaries  of  flowers  that 
have  been  pollinated  from  the  caprifig 
(279,  286).  Crush  one  gently  and  exam- 
ine with  a  lens,  or  under  a  low  power  of 
the  microscope.  It  is  these  "  botanically  " 
Fig.  405.— Vertical  sec-  ripe  fruits  (284)  that  givc  to  the  dried 
mhmte  flo^w^rf  L^ide  Jhe  Ags  of  commcrce  their  plumpness  and 
closed  receptacle.  their  pleasaut,  uutty  flavor.     Why  are 

our  native  American  figs  lacking  in  these  qualities  (279)? 
Could  this  defect  be  remedied?  Do  you  know  of  any 
efforts  being  made  in  that  direction  by  American  cultivators  ? 


406 


407 


408 


409 


Figs.  406-409.  —  Non  caprificated  and  caprificated  figs  :  406,  outside  appearance 
of  non  caprificated  fig  ;  407,  outside  appearance  of  caprificated  fig ;  408,  interior  of 
caprificated  fig  ;  409,  interior  of  non  caprificated  fig. 


306.  Fruit  clusters.  —  Be  careful  not  to  confound  aggre- 
gate and  collective  fruits  with  mere  clusters,  like  a  bunch 
of  grapes  or  of  sumac  berries.  The  distinction  is  not  always 
easy  to  make  out.  The  clump  of  akenes  that  make  up  a  dan- 
delion ball,  for  instance,  though  held  on  a  common  recep- 
tacle, like  the  mulberry  and  other  collective  fruits,  have 
so  little  connection  with  each  other,  and  separate  so  com- 
pletely at  maturity,  as  to  partake  more  of  the  nature  of  a 


FRUITS  269 

cluster  than  of  a  collective  fruit.  The  same  is  true  of  the 
clump  of  tailed  akenes  that  make  up  the  fruit  of  the  clematis. 
Though  the  product  of  a  single  flower  and  thus  technically 
an  aggregate  fruit,  they  are  really  only  a  compact  head  or 
cluster.  Some  degree  of  cohesion  is  necessary  to  constitute 
£,  cluster  of  matured  ovaries  into  an  aggregate  or  a  multiple 
fruit. 

307.  The  individual  fruits  that  make  up  the  various  kinds 
just  described  may  belong  to  any  of  the  classes  mentioned 
in  the  two  preceding  sections :  those  of  the  blackberry,  for 
instance,  are  drupes ;  of  the  strawberry,  akenes ;  of  the 
sweet  gum,   capsules. 


Practical  Questions 

1.  To  what  class  of  fruits  would  you  refer  the  following:  a  banana; 
a  tickseed;  a  dewberry;  a  cocklebur;  a  string  bean;  a  watermelon;  a 
cantaloupe;  a  pomegranate;  a  black  haw;  a  dogwood  berry;  a  red 
pepper  ? 


2.  Tell  which  of  the  following  are  aggregate  or  multiple  fruits,  and 
which  are  fruit  clusters :  an  ear  of  corn ;  of  wheat ;  a  buttonwood  or  a 
sycamore  ball ;  a  hop ;  a  dewberry ;  a  pine  cone ;  a  prickly  pear.  (303, 
304,  306.) 

3.  Tell  the  nature  of  the  individual  fruits  composing  the  different  com- 
binations mentioned  in  the  last  question. 

4.  Can  you  suggest  any  advantage  that  might  accrue  to  a  species  from 
having  its  fruits  clustered  or  compound?     (21,  23,  24,  287.) 


Field  Work 

1.  Study  the  various  edible  fruits  of  your  neighborhood  with  regard  to 
their  means  of  dissemination  and  protection.  Consider  the  object  of  the 
protective  adaptations  in  each  case,  whether  against  heat,  cold,  moisture, 
animals,  etc.  Notice  the  color  of  the  different  kinds,  and  trace  its  sig- 
nificance ;  for  example,  the  bright  red  of  the  holly,  the  dull  color  of  mus- 
cadine, black  haw,  and  wild  smilax.  Account  for  the  prevalence  of  red 
among  autumn  fruits.  Notice  the  position  of  the  fruit  on  the  bough  and 
explain  its  object ;  as,  for  instance,  the  clustering  of  dogwood  at  the  end 
of  the  twig,  the  pendent  position  of  grapes  and  honey  locusts.    Observe 


270  PRACTICAL  COURSE   IN  BOTANY 

the  relation  between  the  color  and  size  of  fruits  and  their  grouping.    What 
advantage  is  it  for  sumac  and  bird  haws  to  be  gathered  in  large  clusters  ? 

2.  Compare  wild  with  cultivated  fruits  and  notice  in  what  respects  man 
has  altered  the  latter  for  his  own  benefit.  Note,  for  instance,,  the  differ- 
ence between  cultivated  apples  and  the  wild  crab,  between  the  cultivated 
grains  and  wild  grasses.  Observe  the  great  number  of  varieties  of  each 
kind  in  cultivation  and  try  to  account  for  it. 

3.  Notice  the  situations  in  which  different  kinds  of  fruits  grow,  whether 
hot,  dry,  moist,  windy,  or  sheltered,  and  how  they  are  affected  by  their 
surroundings.  For  example,  account  for  the  difference  between  black- 
berries growing  on  a  dry  hillside,  and  those  in  moist  land  along  the  borders 
of  a  stream.  Give  the  conclusions  drawn  from  your  observations  in  each 
case. 

4.  Notice  what  animals  feed  upon  the  different  kinds,  and  whether  their 
visits  are  harmful  or  beneficial.  Consider  in  what  respects  the  interests 
of  the  plant  itself,  the  interests  of  man,  and  the  interests  of  other  animals 
may  clash  or  coincide.  Examine  the  vegetation  along  the  hedgerows  and 
borders  of  fields  and  old  fences.  Notice  the  kind  of  plants  that  compose 
it  —  sumac,  sassafras,  cedars,  cat  brier,  etc.  The  list  will  be  slightly 
different  for  different  localities,  but  this  will  not  alter  the  general  conclu- 
sion. What  kinds  of  fruits  and  seeds  do  these  shrubs  produce?  What 
kinds  of  living  creatures  frequent  hedgerows  and  feed  upon  the  seeds  of 
such  plants  ?  Do  you  see  any  relation  between  these  facts  and  one  of  the 
modes  of  seed  dispersal  ? 

5.  Classify  all  the  fruits  you  have  collected  during  your  walk,  under  their 
proper  heads,  as  fleshj^  or  dry,  dehiscent  or  indehiscent,  simple,  accessory, 
aggregate,  collective.  Be  careful  to  distinguish  between  compact  clusters, 
like  the  heads  of  clematis  or  buttonwood,  and  truly  compound  fruits. 


CHAPTER  IX.     THE    RESPONSE   OF   THE   PLANT 
TO   ITS   SURROUNDINGS 

I.     ECOLOGICAL    FACTORS 

Material.  —  A  number  of  small  flowerpots  filled  with  soils  of  as  many 
different  kinds  as  can  be  found  in  the  neighborhood. 

308.  Definition.  —  By  ecology  is  meant  the  relation  of 
plants  to  their  surroundings,  which  may  be  considered  under 
three  general  heads :  their  relations  to  inanimate  nature, 
to  other  plants,  and  to  animals.  The  subject  has  been 
touched  upon  repeatedly  in  the  foregoing  pages,  and,  in 
fact,  it  is  impossible  to  treat  of  any  branch  of  botany  with- 
out some  reference  to  it.  All  that  was  said  about  the  ad- 
justment of  leaves  for  light  and  moisture,  and  their  adap- 
tations for  protection  and  food  storage,  about  the  devices 
for  pollination,  and  for  fruit  and  seed  dispersal,  really 
belong  to  ecology. 

309.  Symbiosis.  —  The  relations  of  plants  to  animate 
nature  are  biological  factors,  and  may  act  in  two  ways: 
(1)  through  the  destruction  of  vegetation  by  hungry  ani- 
mals and  by  parasitic  and  disease-producing  organisms; 
and  (2)  by  associations  for  mutual  benefit,  such  as  are 
described  in  section  viii  of  chapter  VII.  Associations  of 
this  kind  are  included  under  the  general  term  symbiosis, 
a  word  which  means  "  living  together,"  In  its  broadest 
sense  symbiosis  refers  to  any  sort  of  dependence  or  intimate 
organic  relation  between  different  kinds  of  individuals,  and 
so  may  include  the  climbing  and  parasitic  habits;  but  it 
is  usually  restricted  to  cases  where  the  relation  is  one  of 
mutual  benefit.     It  may  exist  either  between  plants  of  one 

271 


272 


PRACTICAL  COURSE  IN  BOTANY 


■1 

^^^!!^SP^''      '^       ;^^ 

S'Sfe^Jj 

M^^0W^^^^ 

Plate  13.  —  Showing  tin;  quick  response  of  vegetation  to  surroundings.  The 
upper  cut  shows  the  appearance  of  an  irrigation  canal  in  the  arid  plains  region, 
when  first  completed  ;  the  lower  cut,  ten  yeara after  completion. 


^•OPEHTYOF 


RESPONSE  OF  THE  PLANT  TO  ITS  SURROUNDINGS     273 

kind  with  those  of  another,  between  animals  with  animals, 
or  between  plants  and  animals,  as  in  the  case  of  the  clover 
and  bumblebee,  and  the  yucca  and  pronuba. 

The  occurrence  of  root  tubercles  on  certain  of  the  legu- 
minosse  (63)  is  a  clear  case  of  symbiosis,  the  microscopic 
organisms  in  the  tubercles  getting  their  food  from  the  plant 
and  at  the  same  time  enabling  it  to  get  food  for  itself  from 
the  air  in  a  way  that  it  could  not  otherwise  do. 

310.  Relations  with  inanimate  nature.  —  But  it  is  to  the 
relations  of  plants  with  inanimate  nature,  and  their  group- 
ing into  societies  under  the  influence  of  such  conditions, 
that  the  term  "  ecology  "  is  more  strictly  applied.  The 
external  conditions  that  lead  to  the  grouping  are  called 
ecological  factors.  The  most  important  of  these  are  tem- 
perature, moisture,  soil,  light,  and  air,  including  the  du-ec- 
tion  and  character  of  the  prevailing  winds.  Each  of  these 
factors  is  complicated  with  the  others  and  with  conditions 
of  its  own  in  a  way  that  often  makes  it  difficult  to  determine 
just  what  effect  any  one  of  them  may  have  in  the  formation 
of  a  given  plant  society. 

311.  Temperature  may  be  even  and  steady,  like  that  of 
most  oceanic  regions,  or  it  may  be  subject  to  sudden  ca- 
prices and  variations,  like  the  "  heated  terms  "  and  "  cold 
snaps  "  that  afflict  our  Eastern  coast  region  every  few  years. 
It  is  not  the  average  temperature  of  a  climate,  but  its 
extremes,  especially  of  cold,  that  limit  the  character  of 
vegetation. 

Temperature  probably  has  more  influence  than  any  other 
factor  upon  the  distribution  of  plants  over  the  globe;  but  it 
can  have  little  or  no  effect  in  evolving  local  difi'erences  in 
vegetation,  because  the  temperature  of  any  given  locality, 
except  on  the  sides  of  high  mountains,  will  ordinarily  be  the 
same  within  a  circuit  of  many  miles. 

312.  Moisture,  again,  may  be  of  all  degrees,  from  the 
superabundance  of  lakes  and  rivers  and  standing  swamps, 
to  the  arid  dryness  of  the  desert,  and  the  water  may  be 


274 


PRACTICAL  COURSE  IN  BOTANY 


still  and  sluggish,  or  in  rapid  motion.  It  may  exist  more 
or  less  permanently  in  the  atmosphere,  as  in  moist  climates 
like  those  of  England  and  Ireland,  where  vegetation  is 
characterizcKl  by  great  verdure;  or  it  may  come  irregularly 
in  the  form  of  sudden  floods,  or  at  fixed  intervals,  causing 
an  alternation  of  wet  and  dry  seasons.  Moreover,  the 
moisture  of  the  soil  or  the  atmosphere  may  be  impregnated 


liotaiiK  al 


with  minerals  or  gases,  which  may  affect  the  vegetation 
independently  of  the  actual  amount  of  water  absorbed. 

Snow  is  a  form  of  water  which  may  act  in  two  entirely 
opposite  ways:  (1)  by  keeping  the  atmospheric  precipita- 
tion locked  up  in  a  solid  state  and  thus  bringing  about  a 
condition  analogous  to  drought  —  for  example,  in  arctic  des- 
erts and  Alpine  snow  fields;  (2)  by  causing  annual  floods 
and  overflows  when  it  melts  in  the  spring,  as  in  the  Nile 
and  Mississippi  valleys. 

In  cold  temperate  regions  it  also  influences  vegetation 


RESPONSE  OF  THE  PLANT  TO  ITS  SURROUNDINGS     275 


Fig.  411.  —  Dogwood,  a  tree  tolerant 
of  shade,  growing  and  blooming  in  a  deeply 
wooded  glen. 


to  a  considerable  extent  by  covering  the  warm  earth  like 
a  blanket  during  winter,  and  thus  protecting  tender  seeds 
and  shoots  that  otherwise  would  not  be  able  to  survive. 

313.  Light  may  be  of  all 
degrees  of  intensity,  from  the 
blazing  sun  of  the  treeless 
plain  to  the  darkness  of  caves 
and  cellars  where  no  green 
thing  can  exist.  Between 
these  extremes  are  number- 
less intermediate  stages :  the 
dark  ravines  on  the  northern 
side  of  mountains,  the  dense 
shade  of  beech  and  hemlock 
forests,  and  the  light,  lacy 
shadows  of  the  pines, — each 
characterized  by  its  peculiar 
form  of  vegetation.  Absence 
of  light,  too,  is  usually  accompanied  by  a  lowering  of  tempera- 
ture and  a  reduction  of  transpiration,  factors  which  tend  to 
accentuate  the  difference  between  sun  plants  and  shade 
plants,  giving  to  the  latter  some  of  the  characteristics  of 
aquatic  vegetation.  Generally,  the 
tissues  of  these  are  thin  and  deli- 
cate, and  having  no  need  to  guard 
against  excessive  transpiration,  they 
wither  rapidly  when  cut  or  exposed 
to  too  great  intensity  of  heat  and 
light. 

314.  Winds  affect  vegetation,  not 
only  as  to  the  manner  of  seed  dis- 
tribution and  the  conveyance  of  pol- 
len, but  directly  by  increasing  transpiration,  and  necessitat- 
ing the  development  of  strong  holdfasts  in  plants  growing 
upon  mountain  sides  and  in  other  exposed  situations.  The 
nature  of  the  region  from  which  they  blow  —  whether  moist, 


Fig.  412. — A  red  cedar  grown 
in  a  barren,  wind-beaten  situa- 
tion. 


276 


PRACTICAL  COURSE  IN  BOTANY 


dry,  hot,  cold,  etc.  —  is  also  an  important 
factor.  In  a  district  open  to  sea  breezes, 
live  oaks,  which  require  a  salt  atmosphere, 
maj^  sometimes  be  found  as  far  as  a  hun- 
dred miles  from  the  coast. 

315.  Soil.  —  While  water  is  the  most  im- 
portant, soil  is  perhaps  the  most  interesting 
of  these  factors  to  the  farmer,  because  it  is 
the  one  that  he  has  it  most  largely  in  his 
power  to  modify.  It  is  to  be  viewed  under 
two  aspects  :  first,  as  to  its  mechanical  prop- 
erties, whether  soft,  hard,  compact,  porous, 
light,  heavy,  etc. ;  secondly,  as  to  its  chemical 
composition  and  the  amount  of  plant  food- 
materials  contained  in  it.     The  first  can  be 

regulated  by  tillage  and  drainage,  the  second  by  a  proper 

use  of  fertilizers. 


Fig.  413.  —  A  red 
cedar  grown  under 
normal  conditions. 


Experiment  92.  To  show  the  influence  of  soil  as  an  ecological 
FACTOR.  —  Fill  a  number  of  small  earthen  pots  with  all  the  different  kinds 
of  soil  that  are  to  be  found  in  your  neighl^orhood.  Keep  well  moistened 
and  make  a  list  of  the  plants  that  appear  spontaneously  in  each.  Is 
there  any  difference  in  the  kinds  produced  by  different  soils  ?  In  vigor 
or  abundance  of  the  same  or  different  kinds  ?  Do  more  seedlings  appear 
in  any  of  the  pots  than  could  live  if  left  alone  ?  What  becomes  of  a  ma- 
jority of  the  seedlings  that  come  up  in  a  state  of  nature  ? 

After  a  time,  stop  watering  until  all  the  plants  are  dead  and  new  ones 
cease  to  appear.  Notice  the  rate  at  which  vegetation  dies  out  in  each 
and  the  kind  of  plants  that  can  live  longest  without  water.  Which  of  the 
different  soils  is  capable  of  sustaining  vegetation  longest  without  a  fresh 
supply  of  moisture  ?    To  what  quality  of  the  soil  is  this  due  ?     (Exp.  53.) 


Practical  Questions 

1.  Is  the  relation  between  man  and  the  plants  cultivated  by  him  a 
symbiosis?     (309.) 

2.  Why  is  it  that  plants  of  the  same,  or  closely  related  species  are  found 
in  such  different  localities  as  the  shores  of  Lake  Superior,  the  top  of  Mt. 
Washington,  and  the  Black  Mountains  in  North  Carolina?     (311,  330.) 


RESPONSE   OF  THE  PLANT  TO   ITS  SURROUNDINGS     277 

3.  Which  of  the  five  ecological  factors  mentioned  in  paragraphs  311- 
315  has  prolmbly  most  largely  influenced  their  distribution? 

4.  What  is  the  prevailing  character  of  the  soil  in  your  neighborhood  ? 

5.  Is  your  climate  moist  or  dry  ?     Warm  or  cold  ? 

6.  Can  you  trace  any  connection  between  these  factors  and  the  pre- 
vailing types  of  vegetation? 

II.    PLANT    ASSOCD^TIONS 

Material.  —  The  subject  is  not  well  suited  to  laboratory  work,  though, 
if  time  permits,  it  is  recommended  that  a  detailed  study  be  made  of  at 
least  one  typical  hydrophyte,  halophyte,  and  xerophyte  plant.  Some 
good  examples  are  :  (1)  Hydrophyte  :  pond  weed,  waterlily,  pipewort  (Erio- 
caulon),  bladderwort,  arrowhead  {Sagittaria) ;  (2)  Halophyte  :  sea  lavender, 
sea  rocket,  sea  lettuce,  water  hyacinth ;  (3)  Xerophyte :  cactus,  century 
plant,  pineapple,  stonecrop,  purslane,  lichen. 

316.  Modes  of  grouping.  —  Plants  group  themselves  in 
their  favorite  habitats,  not  according  to  their  botanical  rela- 
tionships, but  with  regard  to  the  predominance  of  one  or 
more  of  the  ecological  factors  that  influence  their  growth. 
Sometimes  one  or  two  species  will  take  practical  possession 
of  large  areas,  like  the  coarse  grasses  that  spread  over  certain 
salt  marshes,  or  the  pines  that  formerly  constituted  the  sole 
forest  growth  over  extensive  regions  in  North  Carolina  and 
Maine.  Exclusive  growths  of  this  kind  over  limited  areas 
are  sometimes  called  plant  colonies,  and  the  individuals  com- 
posing them  belong,  as  a  general  thing,  to  the  hardy,  pushing 
sort  known  as  "  pioneers,"  which  are  among  the  first  to  take 
possession  of  new  soil  and  force  their  way  into  unoccupied 
territory.  But  more  usually  we  find  a  great  diversity  of 
forms  brought  together  by  their  common  requirements  as 
to  shade,  soil,  moisture,  and  other  external  conditions. 

Any  well-defined  assemblage  of  plants,  whether  of  one  kind 
or  many,  originating  in  such  a  common  response  to  the  same 
influences,  is  called  a  formation.  These  associations  are  va- 
riously classed,  according  to  the  nature  of  their  habitat, 
as  salt  water,  fresh  water,  sand  hill,  swamp,  bog,  river  bot- 
tom, or  such  other  kinds  as  theii'  ecological  character  may 


278 


PRACTICAL  COURSE  IN  BOTANY 


indicate.  Local  conditions  in  limited  areas  may  lead  to  the 
segregation  of  smaller  and  more  compact  groups  called  socie- 
ties. This  term,  however,  is  used  rather  loorsely,  being  treated 
in  some  works  as  synonymous  with  formations,  in  others  as 
analogous  with  what  have  here  been  defined  as  colonies. 

317.  Principles  of  subdivision.  —  The  mixed  associations 
described  in  the  last  paragraph  are  quite  independent  of 


Fig.  414.  —  A  colony  of  Alabama  primroses  {(Enolhcra  specioaa). 

botanical  relationships,  and  any  of  the  factors  named  in 
310,  or  others  of  a  different  kind,  could  be  made  the  basis  of 
their  classification.  They  might  be  grouped,  for  instance, 
according  to  their  economic  uses,  or  according  to  origin, 
whether  native  or  introduced,  as  best  suited  the  purpose  of 
the  classification  in  each  case.  The  moisture  factor,  however, 
has  been  generally  agreed  upon  as  the  one  most  convenient 
for  ordinary  purposes.  Upon  this  principle  plants  are  divided 
into  three  great  groups :  — 


RESPONSE   OF  THE   PLANT   TO   ITS   SURROUNDINGS      279 


Hydrophytes,  or  water  plants,  those  that  requke  abundant 
moisture. 

Xerophytes,  or  drought  plants,  those  that  have  adapted 
themselves  to  desert  or  arid  conditions. 

Mesophytes,  plants  that  live  in  conditions  intermediate 
between  excessive  drought  and  excessive 
moisture.     To  this  class  belong  most  of 
our  ordinary  cultivated  plants  and  the 
greater  part  of  the  vegetation  of  the  globe. 

Halophytes,  "  salt  plants,"  is  a  term 
used  to  designate  a  fourth  class,  based  not 
directly  upon  the  water  factor,  but  upon 
the  presence  of  a  particular  mineral  in  the 
water  or  the  soil  which  they  can  tolerate. 
They  seem  to  bear  a  sort  of  double  rela- 
tion to  hydrophytes  on  the  one  hand  and 
to  zerophytes  on  the  other. 

318.  Hydrophyte  societies.  —  These  em- 
brace a  number  of  forms,  from  those  in- 
habiting swamps  and  wet  moors,  to  the 
submerged  vegetation  of  lakes  and  rivers. 
An   examination   of  almost   any   kind  of 
water  plant  will  show  some  of  the  physio- 
logical effects  of  unlimited  moisture.    Take 
a  piece  of  pondweed,  or  other  immersed 
plant,  out  of  the  water  and  notice  how  com- 
pletely it  collapses.     This  is  because,  being 
buoyed  up  by  the  water,  it  has  no  need  to 
spend  its  energies  in   developing  woody 
tissue.    Floating  and  swimming  plants  will 
generally  be  found  to  have  no  root  system 
or  very  small  ones,  because  they 
their  nourishment  through  all  parts  of  the 
epidermis   directly  from  the   medium  in  which  they  live. 
That  they  may  absorb  readily,  the  tissues  are  apt  to  be  soft 
and  succulent  and  the  walls  of  the  cells  composing  them 


Fig.  415.  —  A  water 
plant  {L  im  nophila) , 
with  water   leaves  and 

absorb  f?""  'fr'  """"^  ^'"'''^'' 

tional  forms. 


280 


PRACTICAL  COURSE   IN   BOTANY 


Fig.  4  1G.  — Seaweed 
(sargassum)  with  blad- 
derlike floats. 


very  thin.  In  some  of  the  pipeworts  (Eriocaulon) ,  the  ells 
are  so  large  as  to  be  easily  seen  with  the  unaided  eye.  If 
you  can  obtain  one  of  these,  examine  it 
with  a  lens  and  notice  how  very  thin  the 
walls  are.  Water  plants  also  contain  nu- 
merous air  cavities,  and  often  develop 
bladders  and  floats,  as  in  the  common  blad- 
derwort  and  many 
seaweeds.  The  leaves 
of  submerged  plants 
are  usually  either 
greatly  reduced  in  size 
or  very  much  cut  and 
divided,  while  the  ones 
that  rise  above  water, 
like  those  of  the  water 
lily,  are  apt  to  be  large 
and  entire,  to  facilitate  floating,  and  have 
stomata  on  their  upper  surface.  Float- 
ing plants  sometimes  form  such  large 
colonies  as  to  be  a  serious  menace  to 
navigation.  Well-known  instances  of 
this  are  the  water  hyacinths  in  the  St. 
John's  River,  Florida,  and  the  vast 
formations  of  swimming  gulfweed  from 
which  the  Sargasso  Sea  takes  its  name. 
319.  Swamp  societies.  —  These  in- 
clude what  may  be  regarded  as  the  am- 
phibious portion  of  the  hydrophyte 
group.  They  compose  the  sedge  and 
cattail  bogs,  reed  jungles,  moss  and  fern 
thickets,  forests  of  cypress,  magnolia, 
black  gum,  pine,  tamarack,  balsam,  and 
the  like.  The  sedges  and  cattails  are  the  pioneers  of  these 
societies,  which  tend  constantly  to  encroach  upon  the  water 
and  so  prepare  the  way  for  the  advance  of  other  colonists. 


Fig.  417. — A  pioneer 
swamp  colony  of  cattails. 
(From  a  photograph  by 
Harry  B.  Shaw,  U.S.  Dcpt. 
Agr.) 


RESPONSE  OF  THE  PLANT  TO  ITS  SURROUNDINGS    281 

Drawing  their  nourishment  from  the  loose  soil  in  which  they 
are  anchored,  and  lacking  the  support  of  a  liquid  medium, 
they  develop  roots  and  vascular  stems.  The  roots  of  plants 
growing  in  swamps  have  difficulty  in  obtaining  proper  aer- 
ation on  account  of  the  water,  which  shuts  off  the  air  from 
them ;  hence  they  are  furnished  with  large  air  cavities,  and 
the  bases  of  the  stems  are  often  greatly  enlarged,  as  in  the 
Ogeechee  lime  {Nyssa  capitata)  and  cypress,  to  give  room 
for  the  formation  of  air  passages.     The  peculiar  hollow  pro- 


FiG.  418.  —  A  Southern  cypress  swami-,  sliowiiiK  on  the  left  the  peculiar  eiilarge- 
mentsfor  aeration,  known  as  "  cypress  knees."    {From  Mo.  Botanical  Garden  Rep't.) 

jections  known  as  "  cypress  knees  "  are  arrangements  for 
aerating  the  roots  of  these  trees. 

320.  Xerophyte  societies  are  adpated  to  conditions  the 
reverse  of  those  affected  by  hydrophytes.  The  extreme  of 
these  conditions  is  presented  by  regions  of  perennial  drought, 
like  our  Western  arid  plains  and  the  great  deserts  of  the  in- 
terior of  Asia  and  Africa.  Under  these  conditions  plants 
have  two  problems  to  solve,  —  to  collect  all  the  moisture  they 
can  and  to  keep  it  as  long  as  they  can.  Hence,  plants  of 
such  regions  have  a  diminished  evaporating  surface,  owing 
to  the  absence  of  foliage  and  the  compacting  of  their  tissues 


282 


PRACTICAL  COURSE  IN  BOTANY 


RESPONSE   OF  THE   PLANT   TO   ITS  STIRROUNDINOS      283 

into  the  stem,  after  the  manner  of  the  cactus  and  prickly 
euphorbia ;  or  their  leaves  may  become  thick  and  fleshy  so 
as  to  resist  evaporation  and  retain  large  amounts  of  mois- 
ture, as  in  the  case  of  the  yucca  and  century  plant.  They 
also  frequently  develop  a  thick,  hard  epidermis,  or  cover 
themselves  with  protective  hairs  and  scales. 

The  principal  types  of  xerophyte  plants  are :  (1)  the  li- 
chens, mosses,  and  saxifrages  found  on  bald  rocks  and  moun- 
tain cliffs  ;  (2)  sand  plants,  such  as  cockspur  grass,  sand  spurry, 
wiregrass,  and  the  like,  inhabiting  sea  beaches  and  pine 
barrens ;  (3)  the  sage  brush,  greasewood,  and  switch  plants 
of  our  Western  alkali  plains ;  (4)  the  cactus  and  yuccas  of 
southern  California,  Arizona,  and  Mexico ;  (5)  the  acacias, 
agaves,  and  hardy  "  chapparal  "  thickets  of  southern  Texas 
and  Mexico.  The  first  class  are  of  importance  as  the  pio- 
neers and  pathfinders  of  the  xerophyte  community.  In 
tropical  and  polar  deserts  alike  they  are  the  first  settlers, 
and  by  aiding  in  the  disintegration  of  rocks  and  their  gradual 
conversion  into  soil,  they  pave  the  way  for  the  coming  of 
the  higher  plants,  and  it  may  be  of  man  himself. 

321.  Partial  xerophytes.  —  Plants  exposed  to  periodic 
and  occasional  droughts  frequently  provide  against  hard 
times  by  laying  up  stores  of  nourishment  in  bulbs  and  root- 
stocks  and  retiring  underground  until  the  stress  is  over. 
This  is  known  as  the  geophilous,  or  earth-loving,  habit. 
Others,  as  some  of  the  lichens,  and  the  little  resurrection 
fern  (Polypodium  incanum,  Figs.  419,  420),  so  common  on  the 
trunks  of  oaks  and  elms  in  the  Southern  States,  make  no 
resistance,  but  wither  away  completely  during  dry  weather, 
only  to  waken  again  to  vigorous  life  with  the  first  shower. 

322.  Physiological  xerophytes.  ^  Plants  growing  in  thin 
or  poor  soil,  such  as  that  on  denuded  hillsides,  fresh  railroad 
cuts,  and  newly  graded  streets,  are  apt  to  take  on  a  more  or 
less  xerophytic  character,  even  though  there  may  be  no  lack 
of  moisture.  Such  soils  are  called  "  now "  because  the 
mineral  elements  in  them  have  not  been  exposed  long  enough 


284 


PRACTICAL  COURSE  IN  BOTANY 


/^n 


Figs.  419,  420.  — A  resurrection  fern  :  419,  in  dry  weather ;  420,  after  a  shower. 


to  have  become  decomposed  and  mixed  with  humus,  and  the 
vegetation  that  first  populates  them  has  to  do  the  pioneer 
work  of  disintegrating  and  impregnating  the  substratum  with 


RESPONSE   OF  THE   PLANT   TO    ITS  SURROUNDINGS    285 


humus.  For  similar  reasons  the  vegetation  of  sandy  bogs 
and  sea  beaches,  owing  to  the  poverty  of  the  soil  in  nitrog- 
enous matter,  usually  develops  xerophyte  adaptations, 
even  though  there  may  be  a  superabundance  of  moisture. 
Plants  growing  on  high  mountain  tops  and  in  cold  arctic 
bogs  take  on  the  same  characteristics  (Fig.  410).  Such  situa- 
tions are  said  to  be  "  physiologically  dry,"  because  the 
moisture  they  have  is  not  in  a  condition  to  be  readily  ab- 


Notico  the  tangle  of  advcii- 
1  from  the  brackish  marsh  soil. 


Fig.  421.  — a   hih.plivti     -u  imi'   -f    i 
titious  prop  roots  M-^i-tiim  m   tin   woik  ■  i    i' 
(From  Mo.  Botanical  Garden  Rep't.) 

sorbed.     The  vegetation  of  arctic  regions  suffers  more  from 
physiological  drought  than  from  cold. 

323.  Halophytes  include  plants  growing  by  the  seashore 
and  the  vegetation  around  salt  springs  and  lakes  and  that  of 
alkali  deserts.  Seaweeds  are  in  a  sense  halophytes,  since 
they  live  in  salt  water,  but  as  they  are  true  aquatic  plants 
and  exhibit  many  of  the  peculiarities  of  hydrophytes  in  their 
mechanical  structure,  they  are  classed  with  them.  The 
name  halophyte   applies  more   particularly  to  lar,d   plants 


286  PRACTICAL  COURSE   IN  BOTANY 

that  have  adapted  themselves  to  the  presence  in  the  soil 
or  in  the  atmospheric  vapor,  of  certain  minerals,  popularly 
known  as  salts,  which  cause  them  to  take  on  many  xero- 
phyte  characteristics.  The  reason  for  this,  as  was  shown  in 
Exp.  39,  is  because  the  mixture  of  salt  in  the  water  of  the 
soil  increases  its  density  so  that  it  is  difficult  for  the  plant  to 
absorb  as  much  as  it  needs,  and  thus  halophytes  are  living 
under  "  physiologically  "  xerophyte  conditions.  If  you  have 
ever  spent  any  time  at  the  seashore,  you  cannot  fail  to  have 
observed  the  thick  and  fleshy  habit  exhibited  by  many  of 
the  plants  growing  there,  such  as  the  samphire,  sea  purslane 
(Sesuvium),  and  sea  rocket  (Cakile).  A  form  of  goldenrod 
found  by  the  seashore  has  thick,  fleshy  leaves,  and  is  as  hard 
to  dry  as  some  of  the  fleshy  xerophytes. 

Another  characteristic  of  desert  plants  that  is  common 
also  to  seaside  vegetation  is  the  frequent  occurrence  of  a 
thick,  hard  epidermis,  as  in  the  sea  lavender  and  saw  grass. 
The  live  oaks,  trees  that  love  the  salt  air  and  never  flourish 
well  beyond  reach  of  the  sea  breezes,  have  small,  thick, 
hard  leaves,  very  like  those  of  the  stunted  oaks  that  grow  on 
the  dry  hills  of  California.  The  presence  of  spines  and 
hairs,  it  will  be  observed,  is  also  very  common ;  e.g.  the  sal- 
sola,  the  sea  oxeye,  and  the  low  primrose  {(Enothera  huvii- 
Jusa).  In  other  cases  the  leaf  blades  are  so  strongly  involute 
or  revolute  (202)  as  to  make  them  appear  cylindrical.  All 
these,  it  will  be  observed,  are  xerophyte  adaptations,  and  the 
object  in  both  cases  is  the  same  —  the  conservation  of  mois- 
ture. 

324.  Mesophytes.  —  These  embrace  the  great  body  of 
plants  growing  under  the  ordinary  conditions  of  temperate 
regions,  which  may  vary  from  the  liberal  water  supply  of 
low  meadows  and  shady  forests  to  the  almost  desert  barren- 
ness of  dusty  lanes  and  gullied,  treeless  hillsides.  The 
forms  and  conditions  they  present  are  so  varied  that  it  vvould 
be  impracticable  to  consider  them  all  in  a  w^ork  like  this,  but 
they  may  be  summed  up  under  the  two  general  heads  of 


RESPONSE  OF  THE  PLANT  TO   ITS  SURROUNDINGS     287 

(1)  open  ground  and  (2)  woodland.  Under  the  first  are  in- 
cluded :  (a)  all  cultivated  grounds  —  fields,  meadows,  lawns, 
pastures,  and  roadsides,  with  their  characteristic  shrubs, 
flowers,  and  grasses;  (6)  heaths  and  plains  of  northern  or 
alpine  regions,  with  their  low,  stunted  perennials  and  bright, 
but  fugacious,  flowers.  Under  the  second  are  classed  all 
woods,  thickets,  and  copses,  with  the  shrubs  and  herbs  that 
form  their  undergrowth.  These  may  be  grouped  in  three 
main  divisions  :  (c)  mixed  forests  of  maple,  ash,  oak,  hickory, 
birch,  sweet  gum,  etc. ;  (d)  pure  forests  of  pine,  balsam,  fir, 
cypress,  and  the  like  ;  and  finally  (e),  the  perennial  splendors 
of  the  tropical  forest,  where  the  vegetation  of  the  globe 
reaches  its  climax  in  luxuriance  and  variety  of  growth. 

Practical  Questions 

1.  Why  do  florists  cultivate  cactus  plants  in  poor  soil?     (320.) 

2.  What  would  be  the  effect  on  such  a  plant  of  copious  watering  and 
fertilizing  ? 

3.  Why  must  an  asparagus  bed  be  sprinkled  occasionally  with  salt? 
(323.) 

4.  If  a  gardener  wished  to  develop  or  increase  a  fleshy  habit  in  a  plant, 
to  what  conditions  of  soil  and  moisture  would  he  subject  it?     (320,  323.) 

5.  What  difference  do  you  notice  between  blackberries  and  dewberries 
grown  by  the  water  and  on  a  dry  hillside  ? 

6.  Are  there  corresponding  differences  in  the  root,  stem,  and  leaves  of 
plants  growing  in  the  two  situations,  and  if  so  account  for  them  ? 

7  When  a  tract  of  dry  land  is  permanently^  overflowed  by  the  building 
of  a  dam  or  levee,  why  does  all  the  original  vegetation  die,  or  take  on  a 
sickly  appearance?     (319.) 

8.  Should  plants  with  densely  hairy  leaves  be  given  much  water,  as 
a  general  thing?     (202,  320.) 

9.  A  farmer  planted  a  grove  of  pecan  trees  on  a  high,  dry  hilltop; 
had  he  paid  much  attention  to  (H!ology  ?    Give  a  reason  for  your  answer. 

10.  Why  do  the  branches  of  trees  often  die,  or  fail  to  develop,  on  the 
windward  side?     (314.) 

11.  Why  do  trees  grown  in  dry  soil  have  harder  wood  than  the  same 
kind  grown  in  wet  soil  ?     (123,  318.) 


288 


PRACTICAL  COURSE  IN  BOTANY 


m.  ZONES  OF  VEGETATION 

325.  The  origin  of  vegetable  zones.  —  The  terms  "  zone  " 
and  "  zonation  "  are  used  to  express  a  general  tendency  of 
plant  societies  and  formations  to  distribute  themselves  in 
more  or  less  regular  belts  or  strata,  relatively  to  the  varying 
intensity  of  the  prevalent  ecological  factor  of  their  habitat. 
In  almost  every  locality  there  exists  some  special  feature  — 
a  pond,  a  brook,  a  small  ravine,  an  isolated  hilltop,  a  deserted 
quarry,  a  gravel  pit,  or  a  railroad  cut,  —  sufficiently  distinct 
from   the   general   surroundings   to   exercise   a   perceptible 

control  over  the 
vegetation  in  its 
immediate  vicinity, 
and  thus  to  become 
the  starting  point 
of  a  series  of  plant 
zones  that  mark  the 
decreasing  influence 
of  the  factor  con- 
cerned, by  their 
change  of  character 
as  they  recede  from 
its  point  of  greatest 
intensity.  Starting 
from  a  barren,  exposed  hilltop,  for  example,  with  a  covering 
of  dry  broom  sedge  (Andropogon)  and  fleabane,  we  encounter 
next  an  almost  desert  zone  of  washed  and  gullied  slopes  in 
whose  hard,  sun-baked  soil  nothing  but  a  few  scrub  pines  and 
brambles  can  gain  a  foothold.  This  will,  perhaps,  be  succeeded, 
by  a  straggling  belt  of  sassafras,  sumac,  and  buckthorn,  mixed 
with  cat  brier  and  blackberry  canes,  beyond  which,  at  the  foot 
of  the  hill,  begins  a  stretch  of  meadow,  or  a  bit  of  woodland 
crossed  by  a  brook,  or  hollowed  into  a  boggy  depression. 
From  this  new  factor  originates  a  second  series  of  zonations, 
passing  through  all  the  stages  of  bog,  swamp,  shade,  and  sun 


Fig.  422. — A  pioneer  colony  of  sumac  growing  on 
a  railroad  cutting.  {From  a  photograph  by  J.  M. 
Coulter.) 


RESPONSE  OF  THE  PLANT  TO  ITS  SURROUNDINGS      289 

plants,  back  to  the  prevailing  type  of  the  region.  Moisture 
is  really  the  controlling  factor  in  both  cases,  its  influence 
in  the  first  being  negative,  —  that  is,  inversely,  —  and  in  the 
other,  positive,  or  directly  proportioned  to  the  quantity 
present. 

326.  Direction  of  zonation.  —  When  the  direction  in  which 
the  controlling  factor  changes  is  horizontal,  as  with  soil  and 
water,  the  zonation  will  be  horizontal;  when,  as  in  the  case 
of  light,  it  is  vertical,  the  zonation  or  stratification  will  be 
vertical.  Examples  of  this  can  be  observed  in  the  growth  of 
almost  any  forest  area,  the  natural  order  of  succession  being  : 
(1)  a  ground  layer  of  mosses  and  fungi ;  (2)  low,  creeping 
vines,  — partridge  berry,  trailing  arbutus,  twinflower  (Linncea) ; 
(3)  small  ferns  and  low  flowering  herbs  —  pyrola,  clintonia, 
trillium ;  (4)  a  zone  of  tall  herbs  and  low  bushes  —  royal 
fern,  cohosh  {Actoea),  blueberries;  (5)  tall  herbs  and  shrubs, 
small  trees,  and  climbing  vines  —  kalmia,  dogwood,  farkle- 
berry,  smilax,  Virginia  creeper ;  (6)  tall  treetops  towering  up 
into  full  sunlight. 

When  the  physical  cause  of  intensity  is  a  central  area,  such 
as  a  pond  or  a  hilltop,  the  zonation  will  be  concentric ;  that  is, 
the  different  belts  will  succeed  each  other  in  widening  circles 
more  or  less  complete.  ^Vhere  the  controlling  cause  extends 
in  a  line,  as  a  river,  or  a  chain  of  mountains,  the  zones  run  in 
parallel  belts  on  each  side  of  it,  and  the  zonation  is  bilateral. 
In  any  case,  however,  it  is  seldom  regular,  being  frequently 
broken  and  interrupted  through  the  intervention  of  other 
factors.  Nor  must  precisely  the  same  kind  of  plants  be 
always  looked  for  in  similar  situations,  though  their  place  is 
usually  occupied  by  kindred  species  and  genera.  The  com- 
mon pitch  pine,  for  instance,  of  the  Northern  sand  barrens 
is  represented  in  sandy  districts  farther  south  by  the  tall, 
long-leaved  pine,  a  kindred  species. 

327.  Succession.  —  Zonation  is  a  regular  succession  of 
different  kinds  of  plants  in  space ;  there  is  also  an  analogous 
succession  in  time,  as,  when  the  vegetation  of  a  locality  is 


290 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  423.  — A  thicket  of  i.iii. 

a  mixed  growth  of  hard  wood  trees. 


killed  off  by  fire  or  other  cause,  plants  of  an  entirely  different 
cliaracter  will  nearly  always  spring  up  to  occupy  its  place.     A 

forest  of  pine,  for  in- 
stance, is  rarely  fol- 
lowed by  conifers, 
but  by  a  growth  of 
hardwood  trees,  and 
vice  versa  —  nature 
thus  giving  an  im- 
pressive example  as 
to  the  effectiveness 
of  a  rotation  of  crops. 
Succession  may  be 
influenced  by  a  va- 
riety of  causes.  Two 
of  the  most  efficient  are  :  (1)  the  exhaustion  of  the  soil  by  the 
long-continued  growth  of  one  formation  (CO),  thus  causing 
a  deficiency  of  mineral  material  suited  for  the  support  of 
plants  of  that  kind ;  (2)  the  migration  of  new  species  into 
the  denuded  territory  where  those  which  have  different  re- 
quirements as  to  min- 
eral nutrients  from  the 
former  inhabitants  will, 
other  things  being  equal, 
have  the  best  chance  to 
succeed. 

328.  Invasion.  —  A 
rapid  and  widespread 
occupation  of  any  terri- 
tory by  a  new  species  is 
called  an  invasion.  No- 
table examples  of  inva- 
ders are  those  of  the 
Russian  thistle  in  the 
northwestern  states  of 


\ 

it. 

r  /  1 

■     s 

^^M 

M 

^f>i^^ 

w^ 

Ti^r     /  ■ 

jH 

^^^p?^*^'" 

m^m> 

^Ir^ 

H| 

^^H^^mi 

p^^';-::^iag%|?B 

nil 

Fig.  424.  —  A  successful  invasion  —  Japanese 
honeysuckle  covering  the  banks  of  a  ravine  and 
climbing  over  shrubs  and  tree  tops. 


the  Union,  and  the  ''  bitterweed  " 
(  Helenium  tenuifolium)  that  has  almost  driven  out  the  hardy 


RESPONSE  OF  THE  PLANT  TO   ITS  SURROUNDINGS      291 

dog  fennel  (Antheinis  cotula)  which  formerly  held  undisputed 
possession  of  arid  places  throughout  the  South  Atlantic  states. 
A  still  more  remarkable  instance  is  the  invasion  of  the  Japa- 
nese honeysuckle  {Lonicera  Japonica),  originally  introduced 
for  ornament,  but  which  has  naturalized  itself  within  the  last 
thirty  years  and  overrun  waste  places  everywhere,  from  the 
Gulf  to  the  Potomac,  with  a  vigor  and  luxuriance  equaled 
by  few  of  our  native  species.  As  its  beauty  and  fragrance 
are  even  more  conspicuous  in  a  state  of  nature  than  under 
cultivation,  and  as  it  can,  moveover,  be  made  very  useful  in 
stopping  gullies  and  washes,  its  phenomenally  rapid  occu- 
pation of  so  large  a  territory  has  caused  no  alarm  and 
consequently  attracted  little  attention. 

329.  Climatic  zones.  —  These  are  more  general  group- 
ings than  those  we  have  been  considering.  They  follow 
in  a  rough  way  thb  parallels  of  latitude,  and  are  classed 
accordingly  as  :  (1)  tropical ;  (2)  subtropical ;  (3)  temperate  ; 
(4)  boreal  or  (on  mountains)  subalpine ;  (5)  arctic  or  (on 
high  mountains)  alpine.  Taking  the  cultivated  plants  of 
our  own  country  by  way  of  illustration,  we  have  the  sub- 
tropical zone,  embracing  Florida  and  the  southern  portion 
of  the  Gulf  states,  where  sugar  cane,  rice,  and  tropical 
fruits  are  the  staple  crops.  Then  comes  the  temperate 
zone,  with  three  agricultural  subdivisions:  (a)  the  great 
cotton  belt,  with  Indian  corn,  sweet  potatoes,  and  the 
peach,  melon,  and  fig  as  secondary  products.  Farther 
north,  in  the  Central  and  Middle  Atlantic  states,  we  find 
(6)  the  region  of  maize,  hemp,  and  tobacco,  with  grapes, 
apples,  pears,  cherries,  and  a  great  variety  of  garden  vege- 
tables as  side  crops.  Finally  comes  (c)  the  great  wheat- 
growing  region  of  the  North,  with  buckwheat,  hay,  and  Irish 
potatoes  as  subsidiary  crops. 

Technically,  the  distribution  of  the  natural  zones  of  vege- 
tation from  south  to  north  is  classed  under  the  three  general 
heads  of  Forest,  Grass  Land,  and  Arctic  Desert,  with  numer- 
ous subdivisions  ill  each. 


292  PRACTICAL  COURSE  IN  BOTANY 

330.  Boundaries  of  the  zones.  —  While  the  broad  conti- 
nental zones  of  vegetation  follow,  in  a  general  way,  the 
climatic  zones  outlined  above,  they  are  not  sharply  defined, 
but  run  into  each  other  and  overlap  in  various  degrees,  so 
that  a  map  depicting  the  range  of  vegetation  in  any  wide 
area  would  show  a  marked  deviation  from  those  of  latitude. 
Various  other  geographical  factors,  such  as  mountain  ranges 
and  bodies  of  water,  influence  the  direction  and  character  of 
the  prevailing  winds  and  rains,  and  through  them  the  mois- 
ture and  temperature,  to  so  great  an  extent  that  they  become 
the  controlling  factors  over  wide  areas.  In  countries  border- 
ing on  the  sea,  the  coast  line  always  marks  a  belt  of  its  own, 
and  on  the  sides  of  a  mountain  range,  all  the  climatic  zones 
from  the  equator  to  the  pole  may  be  repeated  during  an 
ascent  of  a  few  miles. 

In  our  own  country,  where  the  mountain  chains  and  coast 
lines  run  approximately  north  and  south,  the  great  conti- 
nental zones  have  been  superseded,  for  all  practical  purposes, 
by  four  regional  divisions  running  almost  at  right  angles  to 
them.     These  are,  disregarding  minor  subdivisions  :  — 

(1)  The  Forest  region,  occupying  the  eastern  and  south 
central  portion  of  the  Union.  In  classifying  this  territory 
as  forest,  it  is  not  meant  to  imply  that  it  is  now,  or  ever 
was,  one  unbroken  jungle,  like  parts  of  central  Africa,  but 
that  it  combines  the  conditions  most  favorable  to  a  vigorous 
and  varied  forest  growth. 

(2)  The  Plains  region,  extending  from  the  very  irregular 
western  boundary  of  the  forest  region  to  the  Rocky  Moun- 
tains. 

(3)  The  Rocky  Mountain  region,  including  the  Rockies 
and  the  Sierra  Nevadas  with  the  desert  area  between  them. 

(4)  The  Pacific  Slope,  a  narrow  strip  between  the  Sierras 
and  the  Pacific  Ocean. 

The  boundaries  of  these  regions,  like  those  of  the  great 
continental  zones,  overlap  in  various  ways,  the  plants  of  one 
region  often  appearing  in  another,  like  an  arm  of  the  sea 


RESPONSE  OF  THE   PLANT  TO   ITS  SURROUNDINGS    293 


m 

WK^M 

^^^^ 

^^«pi;,.-.^^vf^  ; :  ■ 

^^••'^^^,  ''^"-''  *'' 

l^jp^-v.    .^*| -''"  ■''% 

Plate  15.  —  This  siant  tuli|)  tree  is  a  relic  of  the  primitive  fonst.  It  is  twenty- 
seven  feet  in  circumference,  at  a  distance  of  four  feet  from  the  ground.  Notice  the 
sharp  elbows  of  the  large  boughs,  a  mode  of  branching  characteristic  of  thJ"  kind  of 
tree. 


294  PRACTICAL  COURSE  IN  BOTANY 

projecting  into  the  land.  But  the  district  where  any  class  of 
plants  reaches  its  highest  development  is  its  proper  habitat, 
and  as  a  general  thing  the  one  where  its  cultivation  pays 
best.  It  would  be  a  waste  of  time  and  money  to  try  to  raise 
cotton  in  Maine,  or  cranberries  in  Georgia. 

Practical  Questions 

1.  Does  the  native  wild  growth  of  a  region  furnish  any  indication  of 
the  kind  of  crops  which  could  be  successfully  grown  there?     (325,  326.) 

2.  Can  you  give  a  reason  why  the  zones  of  cultivation  may,  in  some 
cases,  be  more  extensive  than  the  natural  range  of  wild  plants  in  the  same 
region?     (262,  265.) 

3.  Can  you  give  reasons  why  the  reverse  may  sometimes  be  true  ?  (261, 
284.) 

4.  What  crops  are  raised  in  different  parts  of  your  own  state  ? 

5.  Name  some  of  the  native  plants  characteristic  of  different  parts  of 
your  state.     What  are  its  principal  plant  formations? 

Field  Work 

1.  Ecology  offers  the  most  attractive  subject  for  field  work  of  all  the 
departments  of  botany.  It  can  be  studied  anywhere  that  a  blade  of  vege- 
tation is  to  be  found.  In  riding  along  the  railroad,  there  is  an  endless 
fascination  in  watching  the  different  plant  societies  succeed  one  another 
and  noting  the  variations  they  undergo  with  every  change  of  soil  or  climate. 

2.  Students  in  cities  can  find  interesting  subjects  for  study  in  the  vege- 
tation that  springs  up  on  vacant  lots,  around  doorsteps  and  area  railings, 
and  even  between  the  paving  stones  of  the  more  retired  streets.  On  a 
vacant  lot  near  the  public  library  in  Boston,  over  thirty  different  kinds 
of  weeds  and  herbs  were  found,  and  in  the  heart  of  Washington,  D.C.,  on 
a  vacant  space  of  about  twelve  by  twenty  feet,  nineteen  different  species 
were  counted.  Just  where  such  things  come  from,  how  they  get  mto 
such  positions,  and  why  they  stay  there,  will  be  interesting  questions  for 
city  students  to  solve. 

3.  But  the  country  always  has  been  and  always  will  be  the  happy  hunt- 
ing ground  of  the  botanist.  All  the  factors  considered  in  the  two  pre- 
ceding sections  can  hardly  be  found  in  any  one  locality,  but  by  selecting 
areas  traversed  by  brooks,  or  by  gullies  and  ravines,  very  marked  changes 
in  the  character  of  vegetation  may  often  be  observed.  Barren,  sandy, 
or  rocky  soils,  the  sun-baked  clay  of  naked  hillsides,  and  the  borders  of 
treeless,  dusty  roads  will  offer  close  approxunations  to  xerophyte  con- 
ditions. 


i 


RESPONSE  OP  THE  PLANT  TO   ITS  SURROUNDINGS      295 

4.  If  there  are  any  bodies  of  water  in  your  neighborhood,  examine  their 
vegetation  and  see  of  what  it  consists.  Notice  the  difference  in  the  shape 
and  size  of  floating  and  innnersed  leaves  and  acciount  for  it.  Note  the  gen- 
eral absence  of  free-swimming  plants  in  running  water,  and  account  for  it. 
Note  the  difference  between  the  swani])  and  border  plants  and  those  grow- 
ing in  the  water,  and  what  trees  or  shrubs  grow  in  or  near  it.  Compare 
the  vegetation  of  different  bogs  and  pools  in  your  neighborhood,  and 
account  for  any  differences  you  may  observe.  Compare  the  water  plants 
with  those  growing  in  the  dryest  and  barrenest  places  in  your  vicinity, 
note  their  differences  of  structure,  and  try  to  find  out  what  special  adapta- 
tions have  taken  place  in  each  case.  Make  a  list  of  those  in  each  location 
examined  that  you  would  class  as  pioneers. 

5.  Draw  a  map  of  the  vegetation  of  some  locality  in  your  neighborhood 
that  presents  a  variety  of  conditions,  such  as  a  steep  hillside,  a  field  or 
meadow  traversed  by  a  brook,  the  slopes  and  borders  of  a  ravine,  or  the 
change  from  cultivated  ground  to  uncultivated  moor  or  woodland.  Repre- 
sent the  different  zones  and  formations  by  different  colored  inks  or  crayons, 
or  by  different  degrees  of  shading  with  the  pencil. 

6.  Draw  a  map  of  your  state  showing  the  different  agricultural  re- 
gions, as  indicated  by  the  character  of  the  cultivated  plants  in  each; 
use  different  colors,  or  light  and  dark  shading,  to  define  the  boundaries. 
Notice  any  irregularities  of  outline  and  account  for  them  —  whether  due 
to  soil,  moisture,  geological  formation,  winds,  or  temperature.  What  is 
the  controlling  factor  of  each  region  ? 


I 


CHAPTER  X.     CRYPTOGAMS 

I.     THEIR    PLACE    IN    NATURE 

331.  Order  of  development.  —  All  the  forms  that  have 
hitherto  claimed  our  attention  belong  to  the  great  division 
of  Spermatophytes,  or  seed-bearing  plants,  designated  also  as 
Phanerogams,  or  flowering  plants.  They  comprise  the  higher 
forms  of  vegetable  life,  and  because  they  are  more  conspicu- 
ous and  better  known  than  the  other  groups,  they  have  been 
taken  up  first,  since  it  is  more  convenient,  for  ordinary  pur- 
poses, to  work  our  way  backward  from  the  familiar  to  the  less 
known,  rather  than  in  the  reverse  order. 

But  it  must  be  understood  that  this  is  not  the  order  of 
nature.  The  geological  record  shows  that  the  simplest 
forms  of  life  were  the  first  to  appear,  and  from  these  all  the 
higher  forms  were  gradually  evolved.  There  is  no  sharp 
line  of  division  between  any  of  the  orders  and  groups  of 
plants,  but  the  line  of  development  can  be  traced  through  a 
succession  of  almost  imperceptible  changes  from  the  lowest 
forms  to  the  highest,  and  it  is  only  by  a  study  of  the  former 
that  botanists  have  come  to  understand  the  true  nature  and 
structure  of  the  latter. 

332.  Basis  of  distinction.  —  Cryptogams,  or  seedless 
plants  as  a  whole,  are  distinguished  from  the  phanerogams 
by  their  simpler  structure  and  by  their  mode  of  propagation, 
which  in  the  former  is  by  means  of  spores,  while  in  the 
phanerogams  it  is  by  seeds.  A  spore  is  a  simple  organic 
body,  consisting  usually  of  a  single  cell  which  separates  from 
the  parent  plant  at  maturity  and  gives  rise  to  a  new  individual. 
A  seed  is  a  complicated,  many-celled  structure,  containing 
within  itself  the  rudimentary  structure  of  a  new  plant  already 
organized. 

296 


CRYPTOGAMS 


297 


Fig.  425.  —  A  sea- 
weed with  broad,  ex- 
panded thallus. 


Beginning  with  the  simplest  forms,  cryptogams  are  grouped 
in  three  great  orders  :  — 

333.  I.  Thallophytes,  or  thallus  plants.  —  This  group  takes 
its  name  from  the  thallus  structure  that  characterizes  its 
vegetation.  In  its  typical  form,  a  thallus  is 
a  more  or  less  fiat,  expanded  body,  of  which 
the  lichens  and  liverworts  offer  familiar  ex- 
amples among  land  plants,  and  the  kelps  and 
laminarias  among  seaweeds.  It  may  be  of 
any  size  and  shape,  however,  and  sometimes  ^ 
consists  of  a  mere  filament,  as  in  the  com- 
mon brook  silk,  or  even  of  a  single  cell  (Fig. 
429) .  The  term  is  applied  in  general  to  the 
simplest  kinds  of  vegetable  structure,  in 
which  there  is  no  differentiation  of  tissues, 
and  no  true  distinction  of  root,  stem,  and 
leaves.  While  it  is  not  peculiar  to  the  thal- 
lophytes,  it  has  attained  its  most  typical  development  among 
them,  and  the  name  is  therefore  retained  as  distinctive  of 
that  group.  It  embraces  two  great  divi- 
sions, the  Algae  and  Fungi.  The  first 
includes  seaweeds  and  the  common  fresh- 
water brook  silks  and  pond  scums,  be- 
sides numerous  microscopic  forms  whose 
presence  escapes  the  eye  altogether,  or  is 
made  known  only  by  the  discolorations 
(  ^  and  other  changes  caused  by  them  in  the 

KjL^^-^^  water.     To  the  fungi  belong  the  mush- 

FiG.  426.— AnthocG-  Tooms   and  puffballs,   the  molds,   rusts, 

ros,  a  liverwort  with  flat,    niildcWS,     and    the    vast    tribe    of    micro- 
spreading  thallus.  .  .  11      1     7  •  1-1 

scopic  organisms  called  haderia,  which 
are  so  active  in  the  production  of  fermentation,  putrefac- 
tion, and  disease. 

334.  n.  Bryophytes,  or  moss  plants. — This  group  likewise 
contains  two  main  divisions,  Mosses  and  liverworts.  Famil- 
iar examples  of  the  latter  are  the  flat,  spreading  green  plants, 


298 


PRACTICAL  COURSE    IN   BOTANY 


bearing  somewhat  the  aspect  of  Hchens,  met  with  everywhere 

on  wet  rocks  and  banks  around  shady  watercourses.  The 
name  is  a  reminiscence  of  their  former  use 
in  medicine  as  a  specific  for  diseases  of  the 
liver,  and  not,  as  in  the  case  of  the  hver  leaf, 
of  a  fancied  resemblan3e  to  that  organ. 

Mosses  are  one  of  the  best  defined  of 
botanical  orders,  and  ire  easily  recognized 
by  their  slender,  leafy  iruiting  stalks,  grow- 
ing usually  in  dense,  spreading  mats,  and 
presenting  every  appearance  of  a  highly 
organized  structure,  well  differentiated  into 
root,  stem,  and  leaves. 

The  liverworts  represent 
the  more  primitive  division 
of  the  group,  and  in  some 
of  their  forms  approach  so 
near  the  thallophytes  that 
it  is  not  difficult  to  recog- 
nize them  as  connecting 
links  in  the  same  chain  oi 

life.    Their  relationship  to  the  next  higher 

group  is  not  clear,  but  while  they  represent 

a  more  primitive    stage  of  evolution  than 

the  mosses,  the  development  of  the  latter 

has  followed  a  course  divergent  from  the 

main  line  of  evolutionary  progress. 

335.  III.  Pteridophytes,  or  fern  plants,  are 

classed   roughly   in   the   three  divisions  of 

ferns,   horsetails,  and   club  mosses.     They 

differ  greatly  in  structure,  but  all  possess  a 

vascular  system,  and  a  well-organized  struc- 
ture of  root,  stem,  and  leaves.     They  rank 

next  to  the  spermatophytes  in  the  order  of 

development,  and  the  group  is  of  especial  interest  on  account 

of  its  relationship  to  the  higher  plants.     One  of  its  divisions, 


Fig.  427.—. 
shoot  of  peat  mos 
with  ripe  s  p  o  r 
fniits,  /,  /. 


Fig.  428.  —  A  com- 
mon fern  {Poly  po- 
dium vulgare). 


CRYPTOCxAMS  299 

the  club  mosses,  has  probably  given  rise  to  at  least  one  sec- 
tion of  the  gymnospernis,  while  the  ferns  are  regarded  as  the 
ancestors  of  the  true  flowering  plants,  which  make  up  the 
great  class  of  angiosperms,  and  represent  the  highest  type  of 
evolution  yet  attained  in  the  vegetable  kingdom. 

II.     THE    ALGiE 

Material.  —  Simple  forms  of  green  algse  can  be  found  on  the  shady 
side  of  tree  trunks,  damp  walls,  old  fence  palings,  and  the  outside  of  flower- 
pots. Pleurococcus,  one  of  the  commonest  kinds,  occurs  as  a  green, 
powdery  mat  or  felt  in  damp  places,  and  is  often  accompanied  by  proto- 
coccus,  another  good  specimen  for  study.  Spirogyra  and  other  filamentous 
algae  can  be  found  in  stagnant  pools  and  ditches  and  in  old  rain  barrels. 

Appliances.  —  Eosin  solution,  nitric  acid,  alcohol,  iodine  solution ; 
a  white  china  plate ;  a  hand  lens ;  a  compound  microscope,  and  slides. 

336.  Variety  of  forms.  —  This  group  embraces  plants  of 
the  greatest  diversity  of  form  and  structure,  from  the  minute 
volvox  and  desmids  that  hover  near  the  uncertain  boundaries 
dividing  the  vegetable  from  the  animal  world,  to  the  giant 
kelps  of  the  ocean,  which  sometimes  attain  a  length  of  from 
six  hundred  to  one  thousand  feet.  They  are  usually  classed 
according  to  their  color,  as  green,  brown,  and  red  algse, 
including  various  subdivisions  of  each  group.  They  all  con- 
tain chlorophyll,  by  means  of  which  they  manufacture  their 
own  food,  though  in  the  red  and  brown  divisions  it  is  masked 
by  the  presence  of  other  pigments  —  an  adaptation  to  the 
modified  light  that  reaches  them  at  various  depths  under 
water.  With  few  exceptions  they  can  live  only  in  the  water, 
and  unlike  any  other  form  of  plant  life,  attain  their  highest 
development  in  the  salty  depths  of  the  ocean.  The  fresh- 
water forms  are  small  and  inconspicuous,  and  generally  of  a 
more  simple  type  than  the  seaweeds.  The  great  majority  of 
them  belong  to  the  two  classes  of  green  and  blue-green  algse. 
The  former  is  believed  to  have  furnished  the  type  from 
which  the  higher  plants  have  been  evolved. 

337.  Study  of  a  one-celled  alga.  —  Put  a  little  of  the  green 
algae  in  water  on  a  glass  slide.     Hold  up  to  the  light,  or 


300 


PRACTICAL  COURSE  TN  BOTANY 


over  a  sheet  of  white  paper,  and  examine  with  a  hand  lens; 
then  place  under  the  microscope.  It  will  probably  be  found 
to  contain  a  number  of  minute  organisms,  but  ihe  ])leuroc{)Cci 
can  be  recoj^nized  as  small  round  bodies  of  a  briji;ht  ^reen 
color,  some  of  them  separate,  others  adherinji;  togetlier  in 
groups  of  two,  four,  or  more,  with  the  sides  that  are  in  contact 
slightly  flattened.  Each  of  these  bodies  is  an  individual 
plant  consisting  of  a  single  cell,  whence  they  are  said  to  be 
Draw  one  of  the  single  cells  and  one  of  the 
groups,  or  colonies,  as  they  appear 
under  the  microscope.  Try  to  make 
out  the  cell  wall  and  the  nucleus,  and 
label  all  the  parts  (see  7).  If  you 
have  any  difficulty  in  distinguishing 
the  cell  wall,  drop  a  little  glycerine 
or  salt  water  on  the  slide.  This  will 
cause  the  cell  contents  to  shrink  by 
osmosis  (56,  59).  Can  you  make 
out  the  structure  of  the  cell  colonies  ? 

Fig.  429. — Three  stages  in  i-     j  <•  xi_  t 

the  division  of  a  one-celled  alga  They  havc  resulted  from  the  peculiar 

(Glceocapsa   polydermatica)  :    A,   ^^^^  ^f  multiplication  that  prevails 

dmsion  of  a  cell  just  beginning  ; 

B,   division  further  advanced;   amOUg    this   claSS  of    plants.       A    Cell 

ILTil^cont:.."''''""' '"  elongates,  contracts  in  the  middle, 
and  divides  into  two  parts,  each  of 
which  becomes  an  independent  plant  like  the  mother  cell. 
See  if  you  can  find  one  in  the  process  of  division.  The 
daughter  cells  repeat  the  process,  each  one  giving  rise  to  two 
new  individuals,  and  so  on  indefinitely.  The  new  cells  do 
not  always  separate  immediately  on  their  formation,  but  fre- 
quently adhere  together  for  a  time,  in  colonies,  before  falling 
away  and  beginning  an  independent  existence. 

338.  Reproduction  by  fission.  —  This  kind  of  reproduction 
is  called  fission,  or  cell  division,  and  marks  a  very  primitive 
stage  of  development.  Under  stress  of  adverse  conditions 
the  cells  formed  by  division  may  remain  inactive  for  a  time. 
They  are  then  called  re,sting  spores,  and  when  more  favorable 


CRYPTOGAMS  301 

circumstances  arise,  they  begin  again  their  work  of  repro- 
duction and  growth  as  actively  as  ever. 

339.  Meaning  of  the  name.  —  The  suffix  coccus  is  a  Latin 
noun  (plural  cocci)  meaning  a  grain  or  berry,  and  is  a  general 
term  applied  to  any  small,  round  organism  consisting  of  a 
single  cell ;  hence,  micrococcus,  a  minute  round  body ;  proto- 
coccus,  a  primitive  form,  or  prototype  of  one-celled  bodies ; 
and  pleurococcus,  which  may  be  freely  translated  "  a  one- 
sided little  round  body,"  from  the  flattening  of  the  adjacent 
sides  during  fission  —  pleuro  meaning  lateral,  or  pertaining 
to  the  side. 

It  is  important  to  remember  this  definition,  as  the  term 
coccus  is  of  very  frequent  occurrence  in  works  of  biology,  as  a 
suffix  for  designating  small  round  bodies  of  various  kinds. 

340.  Examination  of  a  filamentous  alga.  —  Place  on  a 
white  dish  a  few  drops  of  water  containing  some  of  the  green 
pond  scum  comrrion  in  stagnant  pools  and  ditches.  Exam- 
ine with  a  hand  lens ;  of  what  does  it  appear  to  consist  ? 
Are  the  filaments  all  alike,  or  are  they  of  different  lengths 
and  thickness  ?  Soak  a  number  of  them  in  alcohol  for  half 
an  hour  and  examine  again ;  where  has  the  green  matter 
gone  ?  Do  these  algae  contain  chlorophyll  ?  (336  ;  Exp.  65.) 
This  class  are  called  filamentous  algae  on  account  of  their 
slender,  threadlike  thalli,  which  look  like  bits  of  fine  floss 
floating  about  in  the  water.  The  bubbles  of  oxygen  which 
they  sometimes  give  off  in  great  abundance  cause  the 
frothy  appearance  that  has  given  rise  to  their  popular 
name,  "  frog  spit." 

341.  Spirogyra.  — ^  The  filamentous  algse  are  very  numer- 
ous, and  a  drop  of  pond  scum  will  probably  contain  several 
kinds.  At  least  one  of  these,  it  is  likely,  will  be  a  Spi- 
rogyra, as  this  is  one  of  the  commonest  and  most  widely 
distributed  of  them  all.  Place  a  filament  under  the  micro- 
scope and  notice  the  spiral  bands  in  which  the  chlorophyll 
is  disposed  within  the  cells.  It  is  from  this  spiral  arrange- 
ment that  the  species  takes  its  name.     Do  you  notice  any 


302 


PRACTICAL  COURSE   IN   BOTANY 


430 


431 


roundish  particles  inclosed  in  the  chlorophyll  bands?  Test 
with  a  little  iodine  solution  and  see  what  they  contain. 
Each  filament  will  be  seen,  when  sufficiently  magnified, 
to  consist  of  a  number  of  more  or  less  cylindrical  cells  joined 
together  in  a  vertical  row,  and  thus  forming  the  simple 
threadlike  thallus  which  characterizes  this 
class  of  algse.  Physiologically,  each  cell 
is  an  independent  individual,  and  often 
exists  as  such.  Can  you  see  the  cell 
nucleus?  If  not,  place  a  few  filaments 
in  a  solution  of  eosin  and  add  a  drop  of 
acetic  acid  to  give  the  solution  a  pale 
rose  color.  After  twenty  to  thirty  min- 
utes, examine  again ;  the  nucleus  will  be 
Figs.  430, 431.— <Spi-  stained  a  deep  red.     If  you  can  find  an 

rogyra  (magnified)  :  430,  •         i     xi  j      - 

two  filaments  beginning  uubrokeu  filament,  examine  both  ends  to 
to  conjugate;  431,  for-  gge  whether  there  is  any  differentiation  of 

mation  of  spores.  '' 

base  and  apex. 
342.  Conjugation.  —  See  if  you  can  find  two  filaments 
sending  out  lateral  protuberances  toward  each  other. 
Watch  and  notice  that  after  a  time  these  projections  come 
together  and  unite  by  breaking  down  the  cell  walls  divid- 
ing them,  the  protoplasm  in  each  contracts,  the  contents  of 
one  pass  over  into  the  other,  and  the  two  coalesce,  forming 
a  new  cell  but  little,  if  any,  larger  than  the  original  con- 
jugating bodies.  This  cell  germinates  under  favorable 
conditions  and  produces  a  new  individual.  This  method 
of  reproduction  is  known  as  conjugation.  The  cells  thus  pro- 
duced by  the  union  of  the  contents  of  two  separate  cells 
may  either  germinate  at  once,  and  give  rise  to  new  individ- 
uals, or  remain  quiescent  for  a  time,  as  resting  spores. 


Practical  Questions 

1.  Are  any  of  the  green  algtc  parasitic?     How  do  you  know?     (186, 
336.) 

2.  Why  is  their  pre.sence  in  water  regarded  as  denoting  unhygienic 
conditions  ? 


CRYPTOGAMS 


303 


3.  Mention  some  of  the  ways  in  whicli  their  presence  may  contribute 
to  the  contamination  of  drinking  water. 

4.  Refer  to  Exp.  66,  and  account  for  the  bubbles  and  froth  tliat  usually 
accompany  these  plants  in  the  water. 

5.  Can  you  suggest  any  other  causes  than  the  evolution  of  oxygen  that 
might  produce  the  same  effect  ? 

6.  Is  the  presence  of  these  gas  bubbles  of  any  use  to  floating  plants  ? 


III.     FUNGI 
343.  Classification. —  In  the  fungi  the  thallus  structure 
is  greatly  modified,  appearing  usually  as  a  network  of  fine 
threads  called  the  mycelium 
(pL,  mycelia),  from  a  Greek 
word    meaning    "fungus" 
(369).     These    plants    are 
all,    with   a   few  doubtful 
exceptions,      parasites     or 
saprophytes  which  contain 
no     chlorophyll     and     are 
incapable  of  supporting  an 
independent      existence. 
Biologists  are  divided  as  to 
their  position  in  the  genea- 
logical  tree   of   life.     The 
weight   of    authority 
at  present  inclines  to 
the  view  that  they  are 
degenerate  forms  de- 
rived from  the  algsc, 
but  they  have  been 

so    modified    by   their        ^^^   432. -a  common  form  of  moid,  magnified. 

parasitic  habits  as  to  showing  thallus  modified  into  a  fibrous  mycelium: 

1         , 1     .  • ,  •         a,  a,  spore  cases;  h,  mycelium.    {After  Kopf,  in  part.) 

render  then-  position 

in  the  general  scheme  of  life  a  doubtful  one.  They  repre- 
sent an  offshoot,  or  side  branch,  as  it  were,  of  the  great 
evolutionary  line,  and  so  may  be  considered  for  the  present 
as  standing  apart  in  a  class  by  themselves. 


304  PRACTICAL  COURSE  IN  BOTANY 

344.  Numbers  and  variety.  —  Fungi  exceed  every  other 
class  of  living  organisms  both  in  the  number  of  species  and 
of  individuals  composing  them.  They  include  such  diverse 
forms  as  bacteria,  molds,  rusts,  mildews,  mushrooms,  and 
the  like,  ranging  in  size  all  the  way  from  the  giant  puffball, 
a  foot  or  more  in  diameter,  to  the  almost  inconceivably 
minute  influenza   bacillus,   of  which   nearly  two  thousand 


if 

W0^ 

#■.. 

N 

^        — '**^''"'' . .  ,1^1 

i 

ii 

^1^          '<^^-t-4-^='*^^H 

Fig.  433.  —  Cephalothecium,  a  fungus  parasitic  on  rosehips  —  greatly  magnified. 
{From  Mo.  Botanical  Garden  Rep't.    Photographed  by  Hedgcock.) 

million  can  inhabit  a  single  drop  of  water  without  incon- 
venient crowding ! 

345.  The  parasitic  habit.  —  But  while  their  life  history 
is  obscure  and  hard  to  trace,  the  fungi  are,  as  a  class,  well 
differentiated  by  their  parasitic  habit.  They  contain  no 
chlorophyll,  can  manufacture  no  food,  and  consequently 
have  to  obtain  it  ready-made  from  the  tissues  of  living  or 
dead  animals  and  plants.  On  this  account  thej^  are  active 
agents  in  the  production  of  disease  and  decay,  especially 
certain  of  those  manifold  forms  that  have  been  grouped 


CRYPTOGAMS 


305 


together  under  the  general  head  of  bacteria.  While  not  re- 
sponsible for  all  the  disease  known  to  be  caused  by  living 
organisms,  —  some  very  serious  ones,  such  as  malaria  and 
cattle  fever,  being  due  to  animal  parasites,  —  the  majority  of 
those  that  have  been  most  carefully  investigated  are  traced 
to  the  bacteria,  or  other  fungi.  After  any  of  these  parasites 
have  found  a  lodgment  in  the  body  of  an  organism  whose 
tissues  furnish  them  a  congenial  habitat,  they  multiply  with 
enormous  rapidity,  and  through  the  action  of  certain  poisons 
called  toxins,  which  they  excrete,  give  rise  to  the  most  de- 
structive diseases  in  both  animals  and  plants;  and  no  rational 


Figs.  434-437.  —  Disease-producing  bacteria :  434,  bacteria  of  consumption 
(Bacillus  tuberculosis)  ;  435,  cholera  bacillus  ;  436,  bacilli  of  anthrax,  showing  spores  ; 
437,  typhoid  bacillus. 

sanitary  science  is  possible  without  a  knowledge  of  their 
habits  and  life  history.  Add  to  the  vast  amount  of  human 
suffering  that  is  to  be  laid  at  their  door  the  economic  damage 
done  by  rust  and  smut  fungi,  by  molds  and  blights  and  mil- 
dews, and  we  shall  be  tempted  to  conclude  that  the  "  battle 
of  life"  is  largely  a  struggle  against  these  invisible  foes. 

346.  Useful  fungi.  —  Not  all  fungi,  however,  are  injurious. 
On  the  contrary,  the  great  majority  of  them  are  harmless, 
and  very  many  kinds  are  positively  beneficial  to  man. 
Without  the  yeasts  and  bacteria  of  fermentation  we  could 
not  have  our  bread  and  cheese.  Other  forms  are  active 
agents  in  the  fertilization  of  soils,  it  having  been  estimated 
that  there  are  100,000  or  more  of  these  infinitesimal  la- 
borers at  work  in  every  cubic  centimeter  (about  ^^  of  a 
cubic  inch)  of  virgin  soil !  Even  the  bacteria  of  putrefac- 
tion, which  we  are  accustomed  to  regard  as  the  embodiment 


306  PRACTICAL  COURSE  IN  BOTANY 

of  all  that  is  foul  and  loathesome,  are  engaged  in  an  unceas- 
ing work  as  scavengers,  without  which  life  would  no  longer 
be  possible  on  our  globe,  as  will  be  shown  ui  the  following 
section. 

A.  Bacteria 

Material.  —  A  vessel  of  water  in  which  hay  has  been  left  to  soak  for 
several  hours ;   a  freshly  boiled  iDotato. 

Appliances.  —  A  double  boiler  for  sterilizing ;  a  number  of  clean  glass 
jars  and  bottles ;  cotton  wool  for  stoppers;  a  compound  microscope. 

Culture  Mediums.  —  A  freshly  boiled  ijotato  answers  very  well  for 
ordinary  purposes.  "Bread  mash"  can  be  made  by  drying  some  bread 
crumbs  in  an  oven,  then  mashing  and  mixing  them  to  a  paste  with  boiling 
water ;  sterilize  by  three  successive  heatings  in  a  double  boiler.  A  sterilized 
preparation  of  gelatine  solution  is  the  medium  most  coimnonly  used. 

347.  How  to  obtain  specimens  for  observation.  —  While 
bacteria  are  plentiful  almost  everywhere,  it  is  not  always 
easy  to  capture  them  just  when  and  where  you  want  them. 
For  this  purpose,  put  some  hay  in  water  and  leave  in  a 
warm  place  away  from  the  light  until  the  liquid  becomes 
cloudy  or  a  film  forms  on  the  surface.  This  will  show  that 
bacteria  are  present.  If  it  is  desired  to  study  any  particu- 
lar kind  of  bacterium,  inoculate  one  of  the  culture  mediums 
described  under  "  material,"  or  a  few  drops  of  sterilized 
extract  of  beef,  with  a  small  quantity  of  the  substance  to  be 
examined,  or  with  dust  or  scrapings  from  the  locality  under 
consideration. 

Experiment  93.  By  what  means  are  bacteria  commonly  distrib- 
uted ?  —  Put  a  slice  of  freshly  boiled  potato  into  each  of  three  glass  tum- 
blers and  cover  with  a  filter  of  cotton  wool  held  in  place  by  tying  tightly 
with  a  cord,  or  by  an  elastic  band.  Set  them  all  in  a  vessel  of  water,  bring 
it  to  a  boil,  and  keep  at  that  temperature  for  half  an  hour,  to  sterilize  the 
air  in  the  tumblers.  When  they  have  cooled,  lift  the  cotton  from  (1)  for 
a  minute  or  two  and  then  replace.  Carefully  pass  the  tip  of  a  medicine 
dropper  through  the  filter  of  (2)  so  as  to  prevent  the  entrance  of  unster- 
ilized  air,  and  put  on  the  slice  of  potato  a  small  quantity  of  the  bacterial 
liquid  prepared  as  directed  in  the  last  paragraph.  Leave  (3)  unopened. 
Keep  all  together  in  a  warm,  dark  place  and  observe  at  intervals  of  from 
12  to  24  hours.     Do  any  bacteria  appear  in  (3)  ?     Do  any  appear  on  the 


CRYPTOGAMS  307 

potato  in  (2),  where  the  liquid  was  dropped?  Are  they  more,  or  less 
abundant  than  in  (1)?  Since  cotton  wool  is  entirely  impervious  to  the 
smallest  microorganisms  known,  would  yen  judge  from  this  experiment 
that  bacteria  can  get  into  any  place  unless  carried  there  by  the  air,  or  by 
some  other  means  ? 

Experiment  94.  Can  bacteria  be  carried  by  pure  air  ?  —  On  a 
warm  (and  preferably  cloudy)  day,  put  a  slice  of  potato  on  a  plate,  and 
leave  uncovered  in  an  unused  room  or  closet,  free  from  dust,  and  kept 
carefully  closed.  Put  another  slice  arranged  in  exactly  the  same  way 
in  an  open  window  on  a  dusty  street,  or  in  a  room  that  is  used  and  daily 
swept  and  dusted.  Do  bacteria  appear  in  the  first  plate  ?  In  the  second  ? 
Is  air  free  from  dust  a  good  conveyor  of  bacteria  ? 

Experiment  95.  What  conditions  are  favorable  to  bacterial 
GROWTH  ?  —  Strain  some  of  your  culture  liquid  into  half  a  dozen  small 
bottles  of  the  same  size,  filling  each  about  half  full.  Put  (1)  in  a  dark, 
cool  place  —  on  ice,  if  the  weather  is  warm ;  (2)  in  a  dark,  warm  place ; 
(3)  in  a  warm,  well-lighted  place ;  into  (4)  put  a  drop  of  carbolic  acid,  form- 
ahn,  corrosive  sublimate,  or  boracic  acid,  and  keep  in  a  dark,  warm  place. 
Keep  (5)  in  boiling  water  for  half  an  hour  or  more,  and  then  place  beside 
(2).  Keep  (6)  in  a  freezing  mixture  of  salt  and  ice  for  several  hours,  then 
place  with  (2)  and  (5).  Examine  all  at  intervals  of  from  12  to  24  hours. 
In  which  bottles  is  tha  presence  of  bacteria  indicated  by  cloudiness  of  the 
contained  liquid,  or  the  formation  of  a  surface  film?  In  which  do  they 
appear  first  ?  In  which  most  abundantly  ?  In  which  last,  or  not  at  all  ? 
What  is  the  effect  of  light  and  darkness  on  their  growth?  Of  heat  and 
cold?  Of  disinfectants?  Name  the  circumstances  that  tend  to  hinder 
their  growti},  in  the  order  of  their  efficacy. 

348.  Microscopic  study  of  bacteria.  —  Put  a  drop  of 
hay  infusion  on  a  slide  and  examine  with  the  highest  power 
of  the  microscope.  You  will  see  a  multitude  of  very  small 
glistening  bodies  including  different  kinds  of  bacteria,  a 
majority  of  which  are  probably  the  hay  bacillus,  B.  sub- 
tilis,  shown  in  Figs.  443,  444.  Notice  that  some  forms 
move  about  freely,  while  others  are  non-motile.  Which 
kind  are  the  more  numerous  ?  The  motion  may  he  either  me- 
chanical, resembling  that  of  the  small  dust  particles  we  see 
dancing  about  in  the  sunshine,  or  apparently  voluntary, 
and  caused  by  the  vibration  of  Uttle  whiplike  cilia.  Can 
you  distinguish  the  two  kinds?    Try  to  make  out  clearly 


308 


PRACTICAL  COURSE   IN   BOTANY 


the  different  shapes  you  see.  Some  appear  as  slender 
chains  or  filaments,  but  this  is  due  to  the  individual  cells' 
adhering  together  for  a  time  before  breaking  up  and  begin- 
ning an  independent  existence.  The  small,  rounded  bodies, 
like  a  period  (Fig.  438),  are  cocci;  the  slender,  rod-shaped 
ones  —  sometimes  slightly  curved  (Fig.  440)  —  are  bacilli 
(sing.,  bacillus) ;  the  comma-shaped  ones,  and  those  gener- 
ally  showing   a   slight   spiral   curvature,  are   vibrios    (Fig. 


441  442 

Figs.  438-442.  —  Typical  forms  of  bacteria:  438,  coccus  type;  439,  the  same, 
hanging  together  in  chains  ;  440,  rod-shaped  bacteria  (bacillus  type),  the  clear  areaa 
in  some  of  these  are  spores  ;  441,  forms  of  vibrio  ;  442,  forms  of  spirillum. 

441);  the  spirally  twisted  ones,  like  a  corkscrew  (Fig.  442), 
are  spirilli  (sing.,  spirillum).  These  are  the  principal  forms 
which  it  is  important  to  distinguish  and  remember.  The 
names  are  applied  very  loosely,  however,  in  practice,  bacillus 
being  often  used  as  a  general  term  applicable  to  almost  any 
kind,  —  the  spirillum  of  cholera,  for  instance,  being  com- 
monly known  as  the  cholera  bacillus,  while  by  some  authors 
vibrios  are  ranked  as  a  variety  of  spirillum. 

349.  Life  history  of  a* typical  bacterium.  —  A  pure  culture 
of  the  Bacillus  subtilis  can  easily  be  obtained  by  boiling 
some  of  the  hay  infusion  for  half  an  hour  and  then  leaving 


CRYPTOGAMS 


309 


in  a  warm  place  till  the  usual  indications  of  the  presence 
of    bacteria    appear    (347).      The    spores    of    this    micro- 
organism are  so  resistant  that  they  can  withstantl  the  tem- 
perature of  boiling  water  for  several  hours,  while  those  of 
most  other  forms  of  bacteria  are  killed  by  a  few  minutes' 
exposure  to  it;  hence,  the  crop  that  develops  after  boiling 
will  consist  of  a  pure  culture  of  the 
..-     '.„','-      'V'      hay  bacillus. 
.- ;'V/ ''"',,■      -    '  -     '         In  their  active  state  these  organ- 
'■' -    --'       ,,.  '  ^.    '  isms  will  be  seen  to  consist  of  single- 

''"•':^A-'^^^^     celled,    rod-shaped    bodies,     about 
three  or  four  times  as  long  as  broad, 
and   generally  cohering   in 


443 


ci'mr^^ 


bands  or  filaments,  as  shown 
in  Fig.  444,  c.  The  black  dots 
within  the  cells  are  the 
spores.  Each  individual 
bacterium  produces  but  a 
single  spore,  or  rather  be- 
comes a  spore  itself,  by  the 
contraction  of  its  contents 
and  the  formation  around 
them  of  a  strong  inclosing 
membrane.  On  germinat- 
ing, the  spores  give  rise  to 
little  ciliated,  one-celled  or- 
ganisms called  ■'  swarm 
spores,"  that  swim  about 
freely  in  the  containing  medium  and  multiply  rapidly  for  a 
time  by  cell  division.  After  this  they  pass  again  into  the 
quiescent  state,  ready,  whenever  favorable  conditions  arise, 
to  begin  anew  the  repetition  of  their  life  cycle,  which  is  an 
irregular  alternation  of  cell  division  and  spore  formation. 

350.  Resistance  of  spores.  —  Bacteriologists  are  not  fully 
agreed  as  to  the  cause  of  spore  formation,  some  holding 
that  it  takes  place  only  when  conditions  are  most  favorable 


444 


Figs.  443,  444.  — Hay  bacillus  (/?.  sub- 
tilis)  :  443,  a  portion  of  the  film  from  the  cul- 
ture liquid,  the  black  lines,  c,  being  bacteria 
in  the  vegetative  state  ;  444,  spore  forma- 
tion ;  a,  d,  motile  cells  and  chain  of  cells  :  h, 
non-motile  cells ;  c,  spores  and  chain  of 
spores  from  the  film  e. 


310  PRACTICAL  COURSE   IN  BOTANY 

for  bacterial  growth,  others  claiming  the  reverse.  The 
consensus  of  opinion  at  present  is  toward  the  view  that  the 
spores  are  a  provision  for  tiding  over  periods  of  stress  and 
difficulty.  They  are  capable  of  retaining  their  vitality 
for  a  long  time,  and  are  much  harder  to  kill  than  the  bac- 
terial cells  in  their  ordinary  vegetative  state,  as  was  seen 
in  the  case  of  the  hay  bacillus.  The  spores  of  one  species 
of  potato  bacillus  have  retained  their  vitality  after  four 
hours  of  boiling,  and  those  of  the  typhoid  bacillus  after 
continuous  exposure  to  a  freezing  temperature  for  more 
than  three  months.  The  majority  of  bacteria,  in  their 
vegetative  state,  are,  however,  either  killed  or  rendered 
inert  by  temperatures  ranging  below  10°  or  above  50°  cen- 
tigrade—  equivalent  to  about  50°  and  122°  Fahrenheit, 
respectively.  It  is  easy  to  see  what  important  bearing 
these  facts  have  on  the  process  of  disinfection. 

351.  Reproduction  and  multiplication.  —  The  ordinary 
mode  of  reproduction  in  bacteria,  as  in  other  unicellular 
organisms,  is  by  fission  (337,  338).  As  each  individual 
forms  but  a  single  spore,  no  increase  in  numbers  could  take 
place  by  this  means  alone.  Hence,  while  the  spores  are 
an  important  factor  in  the  preservation  of  the  species  by 
continuing  its  existence  under  conditions  which  the  active 
organisms  could  not  survive,  their  successful  propagation 
depends  on  their  power  of  rapid  multiplication  by  division. 
If  this  process  were  to  go  on  unchecked,  every  hour,  in  an 
unbroken  geometrical  progression,  the  progeny  of  a  single 
bacterium  would,  in  24  hours,  number  nearly  17  million; 
in  25  hours,  34  million ;  in  26  hours,  G8  million,  and  in  five 
days  they  would  cover  the  entire  surface  of  the  globe,  land 
and  sea,  to  a  depth  of  3  feet !  In  ordinary  standard  milk 
sold  by  dairymen,  and  containing,  when  examined,  less 
than  10,000  microbes  to  the  cubic  centimeter,  —  about 
20  drops,  —  the  number  was  found  to  have  increased  after 
24  hours  to  600  million.  It  is  comforting  to  know,  how- 
ever, that  the  majority  of  these  are  of  the  harmless  kinds 


CRYPTOGAMS  311 

which  are  the  active  agents  in  the  making  of  buttermilk 
and  cheese. 

The  effects  of  their  rapid  multipHcation  will  be  better 
appreciated  when  we  consider  that  bacteria  are  the  smallest 
of  known  living  creatures.  If  lOOO  of  the  influenza  bacilli 
were  spread  out  in  a  single  layer  with  their  sides  touching, 
but  not  overlapping,  they  would  not  take  up  more  room 
than  one  of  the  periods  used  in  punctuating  this  book; 
and  a  coccus  concerned  in  a  tubercular  disease  prevalent 


445  446 

Figs.  445,  446.  —  Milk  (highly  magnified) :  445,  pure,  fresh  milk,  showing  fat 
globules  ;  446,  milk  that  has  stood  for  hours  in  a  warm  room  in  a  dirty  dish,  show- 
ing fat  globules  and  many  forms  of  bacteria. 

among  cattle  in  South  America  has  recently  been  discovered, 
of  which  double  that  number  could  be  accommodated  in  the 
same  space. 

352.  Distribution  of  bacteria.  —  Ordinary  air,  when  free 
from  dust,  contains,  on  the  average,  not  more  than  five 
germs  to  the  liter  —  equal  to  about  1  for  every  12  cubic 
inches.  Pathogenic,  or  disease-producing,  germs  seldom 
occur  in  ordinary  fresh  air,  and  even  when  present  are,  under 
ordinary  circumstances,  harmful  only  to  people  whose 
bodies,  by  reason  of  physical  weakness  or  unhygienic  habits, 
offer  a  congenial  soil  for  their  multiplication.  Numerous  in- 
stances are  known  in  which  perfectly  healthy  persons  have 
carried  about  infectious  disease  germs  in  their  bodies  and 
even  transmitted  them  to  others  without  experiencing 
any  inconvenience,  or  even  being  aware  of  their  presence. 


312  PRACTICAL  COURSE   IN  BOTANY 

Among  others,  the  germs  of  pneumonia,  diphtheria,  and 
tuberculosis  are  often  found  in  the  mouth,  nose,  and  sputum 
of  perfectly  healthy  persons.  There  are  also  a  number 
of  bacteria  that  are  regular  inhabitants  of  the  mouth,  some 
of  which  are  the  cause  of  decayed  teeth  and  foul  breath. 
One  form  of  bacterium,  concerned  in  the  production  of  in- 
flammation and  abscesses  (Staphylococcus)  is  so  constantly 
present  on  the  human  epidermis  that  one  authority  has 
declared  it  impossible  to  sterilize  the  skin  so  thoroughly 
as  to  free  it  entirely  of  this  microbe.  It  is  ordinarily  not 
harmful  unless  it  comes  in  contact  with  open  wounds  and 
abrasions. 

353.  The  economic  importance  of  bacteria. — It  is  hard 
to  say  whether  these  organisms  concern  us  most  on  account 
of  the  damages  attributable  to  them  on  the  one  hand,  or 
the  benefits  we  owe  them  on  the  other.  If  they  were  all 
as  harmful  as  the  pathogenic  kinds,  life  would  hardly  be 
possible  on  the  globe,  while  without  their  presence  life 
as  we  know  it  would  have  ceased  to  be  possible  long  ago. 
They  are  nature's  great  army  of  scavengers,  the  sole  agents 
of  decomposition,  without  which  dead  organic  matter  would 
be  subject  only  to  the  slow  changes  by  which  the  rocks 
and  mineral  matter  of  the  earth's  crust  are  disintegrated, 
and  the  undecomposed  bodies  of  the  vast  procession  of 
plants  and  animals  that  have  existed  since  life  first  began 
on  our  globe  would  long  ago  have  cumbered  its  surface  to  such 
an  extent  as  to  render  impossible  the  continued  develop- 
ment of  life  such  as  we  know. 

354.  Sterilization  is  the  process  of  ridding  a  substance 
of  living  microorganisms.  To  do  this  effectively,  the  pro- 
cess must  be  repeated  several  times  at  intervals,  so  as 
to  give  any  spores  that  may  have  survived  previous  applica- 
tions time  to  pass  into  the  vegetative  state,  when  their 
power  of  resistance  is  diminished  and  they  are  more  easily 
destroyed.  The  incubation  period,  as  the  time  required 
for  the  germination  of  the  spores  is  called,  is  different  for 


CRYPTOGAMS  313 

different  kinds  of  bacteria ;  hence  the  importance,  from  a 
sanitary  point  of  view,  of  a  thorough  knowledge  of  their  Ufc 
history. 

355.  Disinfection  is  sterilization  on  a  large  scale,  and 
the  same  principles  apply  to  both.  Heat  is  the  safest 
disinfectant  for  objects  that  will  bear  it,  if  continued  long 
enough  and  repeated  often  enough  at  a  sufficiently  high 
temperature.  Freezing  will  destroy  some  kinds  of  germs 
and  check  or  retard  the  development  of  nearly  all,  but 
is  not  to  be  relied  on  as  a  permanent  germicide,  since 
even  among  flowering  plants  there  are  many  kinds,  not 
only  of  seeds,  but  of  perennial  vegetative  forms  that  are 
capable  of  enduring  an  arctic  temperature  of  many  degrees 
below  freezing  for  long  continued  periods. 

Chemical  disinfectants  act  usually  as  microbe  poisons, 
and  are  unsuitable  as  sterilizers  for  food,  though  valuable 
in  the  purification  of  houses,  clothing,  and  utensils  —  es- 
pecially the  instruments  employed  in  surgical  operations. 

The  prevention  of  the  growth  of  bacteria,  especially  in 
wounds  and  surgical  incisions,  whether  by  means  of  chem- 
ical or  physical  agencies,  is  known  as  antisepsis. 

Practical  Questions 

1.  Wliy  should  a  person  recovering  from  an  ague  continue  for  some 
time  after  to  take  quinine  every  third  or  every  seventh  day?     (350,  354.) 

2.  Name  some  of  the  principal  diseases  produced  by  bacteria. 

3.  What  is  the  principle  to  be  acted  on  in  the  avoidance  of  such  dis- 
eases?    (Exps.  94,  95.) 

4.  Are  the  same  means  equally  effective  for  prevention  and  for  cure  ? 
(354,  355;  Exps.  93-95.) 

5.  Why  is  "fresh  air"  beneficial  in  a  sick  room?     (352;  Exp.  94.) 

G.  Does  it  act  as  a  disinfectant,  or  as  a  mere  diluent  of  the  infected 
air  of  the  room  ?     (352.) 

7.  Why  ought  preserved  fruits  and  vegetables  to  be  scalding  hot  when 
put  into  the  can  ?     (355.) 

8.  Why  is  it  necessary  to  exclude  the  air  from  them?  (Exps.  93, 
94.) 

9.  Reconcile  question  8  with  ciuestion  5. 


314         PRACTICAL  COURSE  IN  BOTANY 

10.  Why  does  the  use,  for  drinking  purposes,  of  water  that  has  been 
boiled  render  a  person  less  liable  to  infectious  diseases?     (355.) 

11.  Was  the  old-fashioned  practice  of  handing  the  baby  round  to  be 
promiscuously  kissed  by  friends  and  neighbors  a  good  one  for  the  baby  ? 
(352.) 

12.  Why  is  the  spitting  habit  to  be  condemned?  The  use  of  common 
drinking  cups  in  schoolrooms  and  other  public  places?     (352.) 

13.  Is  it  proper  from  a  sanitary  point  of  view  that  roommates  at  a  board- 
ing school,  or  even  members  of  the  same  family,  should  use  soap,  towels, 
and  other  articles  of  the  toilet  in  common  ?     (352.) 

B.    Yeasts 

Material.  —  A  piece  of  fresh  baker's  yeast,  some  warm  water,  and  a 
little  honey  or  sugar  solution ;  a  pipette,  or  a  medicine  dropper;  three  or 
four  clean  pint  bottles  or  preserve  jars. 

To  raise  a  crop  of  yeast  fungi  for  observation,  rub  one  fourth  of  a  fresh 
yeast  cake  in  water  enough  to  make  a  paste ;  add  one  pint  of  water,  with 
a  tablespoonful  of  honey  or  sugar,  and  stir  well. 

Experiment  96.  What  conditions  favor  the  growth  of  yeast  ?  — 
Pour  equal  parts  of  the  liquid  made  as  directed  (see  Material)  into  each 
of  three  pint  bottles,  stopper  lightly,  and  label.  Put  (1)  in  a  warm,  dark 
place ;  (2)  in  a  cool,  dark  place ;  and  (3)  in  a  bright  light  in  a  warm  place. 
Observe  at  intervals  of  a  few  hours  the  changes  that  occur  in  each.  Notice 
the  bubbles  that  rise  from  the  liquid.  In  which  bottle  do  they  form  most 
rapidly  ?  Lower  a  lighted  match  into  it,  or  transfer  some  of  the  gas  with 
a  pipette  into  a  vessel  containing  limewater,  and  tell  what  it  is.  Taste 
some  of  the  fermenting  liquid.  Is  it  sweet?  What  has  become  of  the 
sugar  that  was  put  into  it? 

356.  Yeasts  and  ferments.  —  Yeasts  belong  to  a  very  dif- 
ferent order  of  fungi  from  the  bacteria,  but  on  account  of 
their  simpHcity  of  structure  8.nd  the  similarity  of  their  action 
to  that  of  some  of  the  latter,  it  is  usual  to  consider  them  to- 
gether. They  are  the  active  agents  of  fermentation,  and 
include  a  large  number  of  species.  The  kind  used  for  house- 
hold purposes  is  the  same  as  that  employed  in  making  beer. 
Of  this  species  there  are  many  varieties,  each  one  of  which 
gives  a  characteristic  taste  to  the  beer  made  from  it;  and 
brewers,  by  paying  attention  to  the  cultivation  of  yeasts, 
give  their  product  the  special  flavors  peculiar  to  the  different 


CRYPTOGAMS 


315 


brands.  This  kind  of  yeast  is  not  known  to  exist  except  in 
a  state  of  cultivation,  and  probably  owes  its  survival  and 
present  condition  of  development  to  a  symbiosis  with  man, 
on  account  of  its  usefulness  in  bread  making,  and  still  more, 
perhaps,  to  its  part  in  the  gratification  of  his  bibulous  pro- 
pensities, for  among  savage  tribes  the  manufacture  of  fer- 
mented liquors  is  practiced  long  before  the  wholesome  art  of 
bread  making. 

There  are  other  yeasts  existing  in  a  state  of  nature,  such  as 
those  on  the  surface  of  fruits,  which  cause  the  latter,  under 


448 


449 


Figs.  447-449.  — •  Forms  of  common  yeast  (Saccharomyces  cerevisice)  :  447, 
brewers'  yeast ;  448,  household  yeast  (the  large  grains  are  starch)  ;  449,  yeast  from 
beer  sedunent,  showing  budding.     (Figs.  447,  448  X  250  ;  Fig.  449  X  1270.) 

certain  chcumstances,  to  ferment  and  decay.  For  this  reason 
artificial  ferments  are  not  needed  in  making  wine  and 
other  alcoholic  liquors  from  fruits.  Fermentation  is  also 
caused  by  certain  forms  of  bacteria,  as  in  the  formation  of 
vinegar  and  the  souring  of  milk.  Such  bacteria  often  con- 
taminate the  yeast  ferments, 

357.  Microscopic  examination.  —  Place  a  drop  of  the 
cultural  liquid  on  a  slide  and  examine  under  the  highest 
power  of  the  microscope.  ^Yh.SLt  do  you  see?  These  egg- 
shaped  bodies  are  yeast  plants,  unicellular  organisms  like 
the  pleurococcus.  Do  you  see  any  chlorophyll?  Are  the 
yeasts  parasitic?  How  do  you  know?  What  do  they  live 
on  ?  (Suggestion  :  What  food  substance  that  has  disappeared 
was  put  into  the  culture  liquid?)  In  getting  their  nourish- 
ment from  the  sugar,  these  fungi  disintegrate  it  into  alcohol 
and  carbon  dioxide,  which  is  a  process  of  fermentation.     It 


31 G         PRACTICAL  COURSE  IN  BOTANY 

is  the  bubbles  of  gas  that  were  seen  rising  in  the  liquid  which 
cause  beer  to  effervesce  and  bread  to  rise.  They  permeate 
the  dough  and  by  their  expansion  produce  the  sponginess 
peculiar  to  leavened  bread.  Look  for  a  cell  with  a  bud  form- 
ing on  it ;  from  what  part  does  it  appear  to  grow  ?  Where  a 
number  of  buds  remain  for  some  time  attached  to  the  mother 
cell  (Fig.  449),  they  form  a  colony.  Make  a  sketch  of  a 
single  cell  and  of  a  colony  of  two  or  more  adherent  ones, 
labeling  all  the  parts.  If  the  cell  wall  cannot  be  made  out 
clearly,  run  a  little  glycerine,  or  salt  water,  under  the  cover 
glass  with  a  medicine  dropper.  What  causes  the  contents  of 
the  cell  to  contract  and  leave  the  wall?     (56,  59.) 

358.  Reproduction.  —  From  time  to  time  buds  break  away 
from  the  mother  cell  and  form  new  individuals  or  colonies 
of  their  own.  This  process  is  called  multiplication  by  bud- 
ding, and  is  only  another  form  of  cell  division. 

Whenever  reproduction  takes  place  by  other  means  than 
seeds  or  spores,  it  is  said  to  be  vegetative.  This  sort  of  repro- 
duction is  not  confined  to  unicellular  plants,  but  exists  also 
among  the  phanerogams,  the  propagation  of  species  by  means 
of  buds,  tubers,  rootstocks,  runners,  grafting,  and  the  like 
being  variations  of  the  same  process.  On  the  other  hand, 
yeasts  and  bacteria  and  the  unicellular  algae  have  the  power, 
under  extreme  conditions,  to  form  resting  spores,  which 
sometimes  lie  dormant  for  years  and  resume  their  activity 
when  favorable  conditions  return. 

Practical  Questions 

1.  Wlicn  is  fermentation  useful  to  man? 

2.  What  is  the  effect  on  canned  fruits  and  vegetables  if  yeast  cells  get 
into  them? 

3.  Whj^  does  milk  turn  sour  in  warm  weather  ?     (350,  351;  Exp.  96.) 

4.  Whj^  do  buttermilk  and  clabber  spoil  if  left  standing  too  long? 
(345,  356.) 

5.  What  causes  bread  to  be  "heavy"?     (356,  357.) 

6.  Why  will  dough  not  rise  unless  kept  in  a  warm  place  ?     (Exp.  96.) 

7.  Why  is  beer  kept  cold  during  fermentation  ?     (350,  356.) 


CRYPTOGAMS 


317 


C.   Rusts 

Material.  —  A  leaf  of  wheat  affected  with  red  rust ;  a  leaf  or  a  stalk 
with  black  rust.  Some  barberry  leaves  with  yellowish  pustules  on  the 
under  side,  which  under  the  lens  look  like  clusters  of  minute  white  corollas. 
These  are  popularly  known  as  "  cluster  cups."  As  the  spots  on  barberry 
occur  in  spring,  the  red  rust  in  summer,  and  the  black  rust  in  autumn, 
gather  the  specimens  as  they  can  be  found,  and  preserve  for  use. 

The  orange  leaf,  or  brown,  rust  {Puccinia  rubigo-vera)  is  more  common 
in  some  parts  of  the  country  than  the  ordinary  wheat  rust  {Puccinia 
graminis),  but  the  two  are  so  much  alike  that  the  directions  given  will 
do  for  either.  If  the  orange  leaf-rust  (so  named  from  its  color,  and  not 
from  any  connection  with  orange  leaves,  the  logical  relation  of  the  words 
being  orange  leaf-rust,  and  not  orange-leaf  rust)  is  used,  the  cups  and 
pustules  should  be  looked  for  on  plants  of  the  borage  family  —  comfrey, 
hound's-tongue,  etc.  The  orange  leaf-rust  of  apple  is  caused  by  a  fungus 
which  will  serve  to  illustrate  the  same  class  of  parasites. 
The  "teleuto"  stage  of  tliis  will  be  found  on  cedar 
trees,  in  the  excrescences  commonly  known  as  "cedar 
apples";  the  "cluster  cups"  on  the  leaves  of  apple 
and  haw  trees  affected  with  the  disease. 

359.  Red  rust.  —  Uredo  stage.  Examine 
a  leaf  of  "  red  rusted  "  wheat  under  the  lens, 
and  notice  the  little  oblong  brown  dots  that 
cover  it.  These  are  clusters  of  spore  cases, 
and  are  the  only  part  that  appears  above  the 
surface.  Viewed  under  the  microscope,  the 
red  rust  will  be  seen  to  consist  of  a  mycelium 
(see  Fig.  452),  which  ramifies  through  the 
tissues  of  the  leaf  and  bears  clusters  of  single- 
celled  reddish  spores  that  break  through  the 
epidermis  and  form  the  reddish  brown  spots 
and  streaks  from  which  the  disease  takes  its 
name.  These  spores,  falling  upon  other 
leaves,  germinate  in  a  few  hours  and  form 
new  mycelia,  from  which,  in  six  to  ten  days, 
fresh  spores  arise.  Formerly  this  was  thought  to  complete  the 
life  history  of  the  fungus,  to  which  the  name  of  Urcdo  was 
given.   It  is  now  known,  however,  that  the  red  rust  is  merely  a 


450 


Figs.  450,  451.— 
Leaf  of  wheat  af- 
fected with  orange 
leaf-rust  (Puccinia 
rubigo-vera),  uredo 
stage :  450,  upper 
side  of  leaf ;  451, 
under  side. 


318 


PRACTICAL  COURSE   IN   BOTANY 


Pig.  452.  —  Uredo  spores  of  wheat  rust  (Puccinia  graminis), 
magnified.     {From  Coulter's  "  Plant  Structures.") 


stage  in  the  life  cycle  of  the  plant,  and  to  this  stage  the  old 
name  urcdo  is  applied,  the  spores  being  called  uredo-spores. 

360.  Black  rust.  —  Teleuto  stage.     Next  examine  with  a 
lens  a  part  of  the  plant  attacked  by  black  rust.     Do  you 

observe  any 
difference  ex- 
cept in  the 
color?  Do  the 
two  kinds  of 
rust  attack  all 
parts  of  the 
plant  equally? 
If  not,  what 
part  does  each 

seem  to  affect  more  particularly  ?  At  what  season  does  the 
black  rust  appear  most  abundantly  ?  Place  a  section  of  the 
diseased  part  under  the  microscope  and  notice  that  the  dif- 
ference in  color  is  due  to  a  preponderance  of  long,  two- 
celled  bodies  with  very  thick,  black  walls  (Fig.  453).  These 
are  called  teleu- 
tospores,  a  word 
meaning  "  final 
spores,"  be- 
cause they  are 
formed  only 
toward  the  end 
of  the  season. 
They  are  de- 
veloped from 
the  same  my- 
celium with  the 
uredospores, 
and  are  not  a 

product  of  the  latter,  but  collateral  with  them  and  belong  to 
the  same  stage  in  the  life  history  of  the  fungus.  After  they 
appear,  the  uredospores  cease  to  be  developed  at  all,  and 


Fig.  453.  —  Tcleutosporcs  of  wheat  rust,  magnified. 
(From  Coulter's  "Plant  Structures.") 


CRYPTOGAMS 


319 


only  the  dark  teleutospores  are  produced.  These  remain  on 
the  culms  in  the  stubble  fields  over  winter,  ready  to  begin 
the  work  of  reproduction  in  spring.  For  this  reason  the 
teleutos  are  popularly  known  as  "  winter  spores  "  in  contra- 
distinction to  the  uredos,  or  "  summer  spores,"  whose  activity 
is  confined  to  the  warm  months. 

It  was  formerly  supposed  that  black  rust  was  caused  by  a 
different  fungus  from  that  producing  red  rust,  and  to  it  the 
name  Puccinia  was  given.  This  has  been 
rotained  as  a  general  designation  for  all  fungi 
undergoing  these  two  phases,  and  the  par- 
ticular form  of  fungus  that  we  are  now  con- 
sidering is  known  in  all  its  stages  as  Puccinia 
graminis. 

361.  The  nonparasitic  stage.  —  The  for- 
mation of  teleutospores  completes  that  por- 
tion of  the  life  history  of  the  fungus  during 
which  it  is  parasitic  on  wheat  and  grasses  of 
different  kinds.  In  spring  they  begin  to 
germinate  on  the  ground,  each  cell  producing 
a  small  filament,  from  which  arise  in  turn 
several  small  branches.  Upon  the  tip  of 
each  of  these  branches  is  developed  a  tiny 
sporelike  body  called  a  sporidium  (Fig.  454), 
which  continues  the  generation  of  the  rust  ter's  "Plant  stmc- 
fungus  through  the  next  stage  of  its  exist- 
ence. The  filament  which  bears  these  sporidia  is  not  para- 
sitic, but  when  the  sporidia  ripen  and  the  spores  contained 
in  them  are  scattered  by  the  wind,  there  begins  a  second 
parasitic  phase,  which  forms  the  most  curious  part  of  this 
strange  life  history. 

362.  The  aecidium.  —  Examine  next  the  under  side  of 
some  barberry  leaves  (or  comfrey,  etc.,  if  orange  leaf -rust 
is  used)  for  clusters  of  small  whitish  bodies  that  appear 
under  the  lens  like  little  white  corollas  with  yellow  anthers 
in  the  center,    Examine  a  section  of  one  of  these  under  the 


Fig.  454.  —  Tclcu- 
tosporo  germinating 
and  forming  sporidia, 
s,  s.      {From     Coul- 


320 


PRACTICAL  COURSE   IN  BOTANY 


microscope  and  notice  that  the  yellow  substance  is  com- 
posed of  regular  layers  of  colored  spores.  The  corolla-like 
receptacles  containing  them,  popularly  known  as  ''  clus- 
ter cups,"  are  borne  on  a  mycelium  produced  from  the 
spores  described  in  the  last  paragraph.  This  mycelium  is 
parasitic  on  barberry  or  other  leaves,  according  to  the  kind 
of  fungus,  and  was  long  believed  to  be  a  distinct  plant,  to 

which  the  name  ^cid- 
ium  (pi.,  uEcidia)  was 
given.  This  term  is 
now  applied  to  the 
cluster  cups,  and  those 
fungi  which  at  any 
period  of  their  life  his- 
tory produce  them  are 
called  secidium  fungi. 

363.  Spermogonia. 
—  On  the  upper  sur- 
face of  the  leaves  that 
bear  the  secidia,  notice 
some  small  black  dots 
hardly  larger  than  pin 
points,  but  which, 
when  sufficiently  mag- 
nified, appear  as  little 
flask-shaped  bodies  (Fig.  455)  under  the  epidermis.  These  are 
known  as  spermogonia,  or  pycnidia.  When  mature,  they 
break  through  the  epidermis  so  that  the  necks  protrude,  and 
discharge  a  quantity  of  minute  cells  or  spores,  very  like  some 
that,  later  on,  we  shall  find  playing  an  important  part  in  the 
reproductive  processes  of  certain  other  fungi,  and  of  mosses 
and  liverworts.  In  the  rust  fungi,  however,  their  function  is 
not  understood.  They  may  possibly  be  survivals  of  organs 
which  were  once  active  in  the  life  processes  of  the  plant,  but 
have  become  useless  under  changed  conditions.  Do  such 
organs  throw  any  light  on  the  evolutionary  history  of  plants  ? 


Fig.  455. — Section  through  a  barberry  leaf, 
showing  on  the  upper  side  two  spermogonia,  s,s ; 
and  on  the  under  side,  an  secidium,  a. 


CRYPTOGAMS 


321 


364.  Connection  between  barberry  and  wheat  rust.  — 
With  the  discharge  of  the  aecidium  spores,  the  part  of  the 
Hfe  cycle  of  the  fungus  spent  on  the  barberry  conies  to  an 
end,  and  it  is  ready  to  begin  the  uredo-teleuto  stage  over 
again  as  soon  as  it  finds  a  suitable  host.  Where  there  are  no 
barberries,  it  is  capable  of  propagating  without  them,  either 
by  adapting  itself  to  some  other  host  plant,  or  by  omitting 
the  2ecidium  stage  al- 
together. The  para- 
sitic habit  being  an 
acquired  one,  the 
fungus,  like  some  ani- 
mal organisms  that 
we  know  of,  can  often 
be  "educated  "  by 
force  of  circum- 
stances into  tolerat- 
ing, and  even  thriv- 
ing upon,  foods  which 
under  other  circum- 
stances it  would  re- 
ject. The  wheat  rust 
is  known  to  be  ca- 
pable of  propagating 
year  after  year  in  the       F'«-  ^^g-  -  a  spedes  of  "  cedar  apple  '•  {a,m- 

•^  ''  nosporangiim) ,   showing  the  uredo-teleuto  stage  of 

Uredo      stage,      the     the   apple   rust    fungus.     (From   a    photograph    by 

spores    surviving   I'-f- 1"^  J^- Lioyd.) 

through  the  winter  on  volunteer  grains  and  grasses ;  and  in 
no  other  country  in  the  world  does  rust  do  greater  damage 
to  the  wheat  crop  than  in  Australia,  where  the  barberry 
is  practically  unknown.  This  power  of  accommodation 
possessed  by  many  parasites  is  one  of  the  difficulties  the 
agriculturist  has  to  contend  with  in  the  development  of  rust- 
proof varieties. 

365.  Pol3miorphism.  ^  Plants  that  pass  through  different 
stages  in  their  life  history  are  said  to  be  pulyniorphic,  that 


322  PRACTICAL  COURSE  IN  BOTANY 

is,  of  many  forms.  The  habit  is  very  common  among  the 
lower  forms  of  vegetation.  The  fact  that  one  or  more  of 
the  phases  are  sometimes  omitted,  as  the  secidium  phase 
of  wheat  rust  in  warm  cHmates,  suggests  the  idea  that  it 
may  be  of  use  in  helping  the  plant  to  tide  over  difficult 
conditions.  Besides  giving  better  chances  of  obtaining 
nourishment,  it  probably  has  the  same  effect  as  cross  fer- 
tilization among  flowering  plants,  in  imparting  increased 
strength  and  vitality  to  the  succeeding  generation.  Wheat 
rust  produced  from  barberry  secidia  is  said  to  be  much  more 
vigorous  —  and  consequently  more  destructive  —  than  when 
derived  from  a  uredo  that  has  reproduced  itself  for  several 
generations. 

366.  The  damage  done  by  rust  to  the  host  is  through  the 
destruction  of  its  tissues  by  the  mycelium.  The  chlorophyll 
is  destroyed  so  that  the  plant  can  no  longer  manufacture 
food,  and  is  too  starved  to  produce  good  grain.  There  are 
many  varieties  of  wheat  rust,  which  have  been  found  on 
twenty-seven  different  kinds  of  grain.  Most  of  them  are 
specialized  to  a  particular  host  plant  and  will  not,  ordinarily 
(364) ,  infest  any  other.  Has  this  fact  any  bearing  upon  the 
production  of  rustproof  varieties  ? 

Practical  Questions 

1.  Is  a  farmer  wise  to  leave  scabby  and  mildewed  weeds  and  bushes 
in  the  neighborhood  of  his  grain  fields?     (364,  365.) 

2.  Are  there  any  objections  to  the  presence  of  volunteer  grain  stalks 
along  roadsides  and  in  fence  corners  during  winter?     (364.) 

3.  Should  cedar  trees  be  allowed  to  grow  near  an  apple  orchard  ?  Give 
a  reason  for  your  answer,     (p.  317,  Material.) 

4.  Should  diseased  plants  be  plowed  under  ?     (361.) 

5.  What  disposition  should  be  made  of  them? 

6.  Ought  diseased  fruits  to  be  left  hanging  on  the  tree? 

7.  Why  is  it  necessary  to  pick  over  and  discard  from  a  crate  or  bm  all 
decaying  fruits  and  vegetables? 

8.  Does  a  rotation  of  crops  tend  to  prevent  the  spread  of  disease  in 
plants  ?    Give  reasons  for  your  answer. 

9.  Are  rustproof  varieties  to  be  relied  on  indefinitely  ?     (364.) 


CRYPTOGAMS  323 

D.    Mushrooms 

Material.  —  Any  kind  of  gilled  mushroom  in  different  stages  of  de- 
velopment, with  a  portion  of  the  substratum  on  which  it  grows,  contain- 
ing some  of  the  so-called  spawn.  The  common  mushroom  sold  in  the 
markets  {Agaricus  campestris)  can  usually  be  obtained  without  difficulty. 
Full  directions  for  cultivating  this  fungus  are  given  in  Bulletin  53  of  the 
U.  S.  Department  of  Agriculture.  From  6  to  12  hours  before  the  lesson 
is  to  begin,  cut  the  stem  from  the  cap  of  a  mature  specimen,  close  up  to 
the  gills,  lay  it,  gills  doAvnward,  on  a  piece  of  clean  paper,  cover  with  a  bowl 
or  pan  to  keep  the  spores  from  being  blown  about  by  the  wind,  and  leave 
until  a  print  (Fig.  466)  has  been  formed. 

367.  Mushrooms  and  toadstools.  —  The  popular  distinc- 
tion which  limits  the  term  "  mushroom  "  to  a  single  species, 
the  Agaricus  campestris,  and  classes  all  others  as  toadstools, 
has  no  sanction  in  botany.  All  mushrooms  are  toadstools 
and  all  toadstools  are  mushrooms,  whether  poisonous  or 
edible.  The  real  distinction  is  between  mushrooms  and 
puffballs,  the  former  term  being  more  properly  applied  to 
fungi  which  have  the  spore-bearing  surface  exposed. 

368.  Examination  of  a  typical  specimen.  —  The  most 
highly  specialized  of  the  fungi,  and  the  easiest  to  observe  on 
account  of  their  size  and  abundance,  are  the  mushrooms 
that  are  such  familiar  objects  after  every  summer  shower. 
The  gilled  kind  —  those  with  the  rayed  laminae  under  the 
cap  —  are  usually  the  most  easily  obtained.  Specimens 
should  be  examined  as  soon  after  gathering  as  possible,  since 
they  decay  very  quickly. 

369.  The  mycelium.  —  Examine  some  of  the  white  fibrous 
substance  usually  called  spawn  through  a  lens.  Notice 
that  it  is  made  up  of  fine  white  threads  interlacing  with  each 
other,  and  often  forming  webby  mats  that  ramify  to  a  con- 
siderable distance  through  the  substratum  of  rotten  wood 
or  other  material  upon  which  the  fungus  grows.  This  webby 
structure,  often  mistaken  for  root  fibers,  is  the  thallus  or 
true  vegetative  body  of  the  plant,  the  part  rising  above 
ground,  and  usually  regarded  as  the  mushroom,  being  only 
the  fruit,  or  reproductive  organ.   Place  some  of  the  mycelium 


324 


PRACTICAL  COURSE  IN  BOTANY 


Fig.  457.  —  Mycelium 
of  a  mushroom  (Agaricus 
campestris),  with  young 
buttons  (fruiting  organs) 
in  different  stages  :  1,  2, 
3,  4,  5,  sections  of  fructi- 
fication at  successive  pe- 
riods of  development;  m, 
mycelium  ;  st,  stipe  ;  p, 
pileus ;  I,  gill,  or  lamina  ; 
V,  veil. 


under  the  microscope  and  notice  that  it  is 
composed  of  deHcate  filaments  made  up  of 
single  cells  placed  end  to  end,  as  in  Spi- 
rogyra  (341),  These  filaments  are  called 
hyphoe. 

370.  The  button.  —  Look  on  the  my- 
celium for  one  of  the  small  round  bodies 
called  buttons  (Fig.  457).  These  are  the 
beginning  of  the  fruiting  body  popularly 
known  as  the  mushroom,  and  are  of  va- 
rious sizes,  some  of  the  youngest  being 
barely  visible  to  the  naked  eye.  After  a 
time  they  begin  to  elongate  and  make 
their  way  out  of  the  substratum. 

371.  The  veil  and  the  volva.  —  Make  a 
vertical  section  through  the  center  of  one 
of  the  larger  buttons  after  it  is  well  above 
ground,  and  sketch.     Notice  whether  it  is 

entirely  enveloped  from  root  to  cap  in  a  covering  membrane 
—  the  volva  (Fig.  458,  a)  —  or 
whether  the  enveloping  mem- 
brane extends  only  from  the 
upper  part  of  the  stem  to  the  b-, 
margin  of  the  cap  —  the  veil  (Fig. 
458,  d) ;  whether  it  has  both  veil 
and  volva,  or  finally,  whether  it 
is  naked,  that  is,  devoid  of  both. 
372.  The  stipe,  or  stalk. — 
Notice  this  as  to  length,  thick- 
ness, color,  and  position;  that  is, 
whether  it  is  inserted  in  the 
center  of  the  cap  or  to  one  side 
(excentric),  or  on  one  edge  (lat- 
eral).   Observe  the  base,  whether       yi^i.  458. —  Diagram  of  umx- 

bulboUS,     tapering,      or     straight,     panded  ^mamVa.  sho^dng  parts:    a, 
111  volva;  b,  pilcus;  c,  gills  ;  d,  veil ;  e, 

and   whether  surrounded   by  a   stipe ;  m,  myceUum. 


CRYPTOGAMS 


325 


Fig.  459.  —  Parasol 


cup,  or  merely  by  concentric  rings  or  rag- 
ged bits  of  membrane  (the  remains  of  the 
volva).  Look  for  the  aniiulus  or  ring  (re- 
mains of  the  veil)  near  the  insertion  of  the 
stipe  into  the  cap,  and  if  tliere  is  one,  notice 
whether  it  adheres  to  the  stipe,  or  moves 
freely  up  and  down  (Fig.  459,  a)  ;  whether 
it  is  thick  and  firm,  or  broad  and  membra- 
nous so  that  it  hangs  like  a  sort  of  curtain 
round  the  upper  part  of  the  stipe  (Fig. 
467,  a) .  Break  the  stem  and  notice  whether 
it  is  hollow  or  solid;  observe  also  the  texture, 
whether   brittle,    cartilaginous,   fibrous,   or  mushroom    (Lepiota 

f.      .  procera),  showing 

Ilesny.  movableannulus:  *7, 

373.  The  pilaus,  or  cap.  —  Observe  this  as  ^^ipe ;  «,  annuius.  or 

*"*'  *  '  *  ring;  u,  umbo;  p,  p, 

to  color  and  surface,  whether  dry,  or  moist  floccose  patches  left 
and  sticky ;  smooth,  or  covered  with  scurf  ^^  ^°  ^^' 
or  scales  left  by  the  remains  of  the  volva,  as  it  was  stretched 
and  broken  up  by  the  expanding  cap  (Fig.  459,  p,  p).  Note 
also  the  size  and  shape,  whether  coni- 
cal, expanded,  funnel-shaped  (Fig.  460), 
or  umhonate  —  hsiving  a  protuberance 
at  the  apex  (Fig.  459)  —  or  whether  the 
margin  is  turned  up  at  the  edge  (revo- 
lute,  Fig.  467),  or  under  (involute,  Fig. 
459). 

374.  The  gills,  or  lairjjnae.  —  Look  at 
the  under  surface  and  notice  whether 
the  gills  are  broad  or  narrow,  whether 
they  extend  straight  from  stem  to  mar- 
gin, or  are  rounded  at  the  ends,  or 
infundibuiiform  piieus  and  curvcd,  toothcd,  or  lobcd  iu  any  way. 
Notice  their  attachment  to  the  stipe, 
whether /ree,  not  touching  it  at  all ;  adnate,  attached  squarely 
to  the  stem  at  their  anterior  ends;  or  decurrent,  running 
down  on  the  stem  for  a  greater  or  less  distance  (Fig.  460). 


Fig.  400.  —  Chanterelle 
{Cantkarellus  cibarius),  with 


326 


PRACTICAL  COURSE  IN  BOTANY 


375.  The  hymenium.  —  Cut  a  tangential  section  through 
one  side  of  the  pileus  and  sketch  the  section  of  the  gills  as 
4^5.5  they  appear  under  a  lens,  or  a  low 

power  of  the  microscope.  Notice 
that  the  blade  consists  of  a  central 
portion  called  the  trama  {Ir,  Fig.  462) 
and  a  somewhat  thickened  portion, 
h,  constituting  the  hymenium,  or 
spore-bearing  surface.  Now  exam- 
ine, under  a  high  power,  a  small  sec- 
tion from  the  edge  of  a  gill,  including 
a  bit  of  the  trama.  Notice  that  this 
last  consists  of  a  tissue  of  mycelial 
cells  (Fig.  463)  covered  by  the  hy- 
menium, or  spore-bearing  membrane, 
which  is  thickly  clothed  with  a  layer 
of  elongated,  club-shaped  cells  (6,  h 
and  p,  p,  Fig.  463)  set  upon  it  at  right 
angles  to  the  surface.  Some  of  these 
put  out  from  two  to  four,  or  in  some 
species  as  many  as  eight,  little 
prongs,  each  bearing  a  spore  (s,  s,  Fig. 


Figs.  461-463.  —  Section  of  a 
gilled  mushroom  :  461,  through 
one  side,  showing  sections  of  the 
pendent  gills,  g,  g  (slightly  mag- 
nified) ;  462,  one  of  the  gills 
more  enlarged,  showing  the  cen- 
tral tissue  of  the  trama,  tr,  and 
the  broad  border  formed  by  the 
hymenium,  h  463,  a  small  sec- 
tion of  one  side  of  a  gill  very 
much  enlarged,  showing  the 
club-shaped  basidia,  b,  b,  stand- 
ing at  right  angles  to  the  surface, 
bearing  each  two  small  branches 
with  a  spore,  s,  s,  at  the  end. 
The  sterile  paraphyses,  p,  are 
seen  mixed  with  the  basidia. 


463),  while  others  re- 
main sterile.  The  spore- 
bearing  cells  are  called 
basidia;  the  steri  e 
ones,  paraphyses;  and 
the  whole  spore-bearing  surface  together,  the  hymenium,  from 
a  Greek  word  meaning  a  membrane.    It  is  from  the  presence 


Figs.  464,  465.  —  A  tube  fungus  (Boletus  edidis)  : 
464,  entire ;  465,  section,  showing  position  of  the 
tubes. 


CRYPTOGAMS 


327 


Fig.  466.  —  Spore  print  of  a 
gilled  mushroom. 


of  this  expanded  fruiting  membrane  that  the  class  of  mush- 
rooms we  are  considering  gets  its  botanical  name,  Hymeno- 
mycetes,  membrane  fungi.  The  hymenium  is  not  always 
borne  on  gills,  but  is  arranged  in  various  ways  which  serve 
as  a  convenient  basis  for  distinguishing  the  different  orders. 
In  the  tube  fungi,  to  which  the  edible 
boletus  belongs  (Figs.  464,  465),  the 
basidia  are  placed  along  the  inside  of 
little  tubes  that  line  the  under  side 
of  the  pileus,  giving  it  the  appear- 
ance of  a  honeycomb.  In  another 
order,  the  porcupine  fungi,  they  are 
arranged  on  the  outside  of  project- 
ing spines  or  teeth,  while  in  the 
morelles  they  are  held  in  little  cups 
or  basins. 

376.  Spore  prints.  —  When  the 
gills  are  ripe,  they  shed  their  spores  in  great  abundance. 
Take  up  the  pileus  that  was  laid  on  paper,  as  directed  under 
Material,  on  page  323,  and  examine 
the  print  made  by  the  discharged 
spores;  it  will  be  found  to  give  an 
exact  representation  of  the  under  side 
of  the  pileus. 

377.  The  spores.  —  Notice  the  color 
of  the  spores  as  shown  in  the  print. 
This  is  a  matter  of  importance  in  dis- 
tinguishing gill-bearing  fungi,  which  are 
divided  into  five  sections  according  to 
the  color  of  the  spores.  One  source  of 
danger,  at  least,  to  mushroom  eaters 
(/™°«„SV«Srsrow!  would  be  avoided  if  this  difference  was 
ing  the  broad  pendent  annu-   always    attended   to,    for   the   deadly 

lus,  a,  formed  by  the  rup-  -j.       /  a  -j  i     n    ■  i     \  i    ii 

tured  veU;  the  cup  at  the   amauita  {Amanita  p/iaUoides)  and  the 
base  c,  and  fioccose  patches   almost  CQually  daugcrous  fly  mushroom 

on  the  pileus,  left   by  the  i  ^  o  j 

breaking  up  of  the  volva. 


{A.  muscaria)  both  have  white  spores, 


328 


PRACTICAL  COURSE  IN  BOTANY 


while  the  favorite  edible  kind  (Agaricus  campestris),  though 
white-gilled  when  young,  produces  dark,  purple-brown  spores 
that  cannot  fail  to  distinguish  it  clearly  for  any  one  who  will 
take  the  trouble  to  make  a  print. 

378.  Economic  properties.  —  Most  of  the  wood-destroy- 
ing fungi  belong  to  this  and  allied  orders.  They  are  among 
the  worst  enemies  the  forester  has  to  deal  with  (140),  and 

millions  of  feet  of 
lumber  are  destroyed 
every  year  by  them. 

Over  seven  hun- 
dred kinds  of  fungi 
growing  in  the  United 
States  have  been  de- 
scribed as  edible,  but 
the  evil  repute  into 
which  the  whole  class 
has  been  brought  by 
the  poisonous  quali- 
ties of  a  few  species, 
and  the  difficulty,  to 
any  but  an  expert,  of 
distinguishing  be- 
tween these  and  the  harmless  kinds,  has  caused  them  to  be 
generally  neglected  as  articles  of  diet.  While  they  are 
pleasant  relishes  and  furnish  an  agreeable  variety  to  our  daily 
fare,  their  food  value  has  been  greatly  exaggerated.  They 
contain  a  large  proportion  of  water,  often  over  90  per  cent, 
and  the  most  valued  of  them,  the  Agaricus  campestris,  is 
about  equivalent  to  cabbage  in  nutrient  properties. 


Fig.  468.  —  Portion  of  the  root  of  a  maple  afifected 
with  rot  caused  by  the  mycelium  of  a  fungus  that 
has  penetrated  to  its  interior. 


Practical  Questions 

1.  Why  are  mushrooms  generally  grown  in  cellars?     (186,  343.) 

2.  Name  any  fungi  you  know  of  that  are  good  for  food  or  medicine  or 
any  other  purpose. 

3.  Name  the  most  dangerous  ones  you  know  of. 


CRYPTOGAMS 


329 


4.  Do  you  find  fungi  most  abundant  on  young  and  healthy  trees,  or 
on  old,  decrepit  ones  ?    Account  for  the  difference.     (141,343,378.) 

5.  Do  you  ever  find  them  growing  on  perfectly  sound  wood  anywhere  ? 

6.  Are  they  ever  beneficial  to  a  tree  ?     (86.) 

7.  Is  it  wise  to  leave  old,  unhealthy  trees  and  decaying  trunks  in  a 
timber  lot? 

rV.    LICHENS 

Material.  —  Specimens  can  be  found  almost  everywhere,  growing 
on  rocks,  walls,  logs,  stumps,  and  trees.  Some  of  the  more  common  kind 
are :  Parmelia,  recognizable  by  the  shallow  spore  cups  borne  on  the  upper 
surface  of  the  thallus;  Cladonia,  by  the  little  stalked  receptacles,  like 
goblets,  in  which  its  spores  are  held ;  Physcia,  by  its  bright  orange  color. 
Where  practicable,  it  is  well  to  have  several  different  kinds  for  comparison. 
Iceland  moss  {Cetraria  islandica)  can  generally  be  obtained  from  the 
grocers,  and  is  a  good  example  of  an  intermediate  form  between  foliaceous 
and  fruticose  lichens. 

If  the  specimens  are  very  dry,  they  will  be  too  brittle  to  handle  conven- 
iently, and  should  be  moistened  by  soaking  a  short  time  in  water.  This 
will  render  them  quite  flexible  and  also  bring  out  the  green  color  more 
clearly. 

379.  Examination  of  a  typical  specimen.  —  The  com- 
monest kind  of  lichens,  and  generally  the  most  easily  ob- 


FiG.  469.  —  Foliaceous  lichens:  A,  Xanthoria  (Physcia)  parietina;  B,  Parmelia 
conspersa;  a,  spore  cups. 

tained,  are  those  that  grow  on  rocks  and  tree  trimks  in  flat, 
spreading  patches.     Their  margins  are  much  dented  and 


330 


PRACTICAL  COURSE  IN  BOTANY 


curled,  giving  them  a  somewhat  leaflike  appearance,  whence 
they  are  called  "  foliaceous  "  lichens.  This  broad,  expanded 
body  is  the  thallus,  or  vegetative  part,  as  distinguished  from 
its  reproductive  part.  Examine  carefully  the  thallus  of 
your  specimen.  Note  the  size  and  shape  of  the  indentations. 
Is  there  any  order  or  regularity  about  them,  such  as  was 
observed  in  the  lobing  of  leaves?  Is  there  any  difference 
in  color  between  the  upper  and  under  sides?  What  other 
differences  do  you  notice?  Do  you  see  anything  like  hairs, 
or  rootlets,  on  the  under  side  ?  Mount  one  of  them  in  water 
and  place  under  the  microscope.  WTiat  does  it  look  like? 
Compare  with  one  of  the  hairs  from  a  leaf  of  mullein,  grom- 
well,  blueweed,  or  other  hairy  plant,  with  the  hypha  of  a 
fungus  mycelium,  and  with  your  study  of  the  root  hair  in 
67  (a).  Is  it  a  hair  or  a  root?  These  rootlike  hairs  are 
called  rhizoids,  and  serve  to  anchor  the  lichen  to  its  substra- 
tum. Look  on  the  upper  side  for  little  cup-shaped  or 
saucer-shaped    receptacles.     On  what   part   of   the   thallus 

are  they  situated?  Ex- 
amine with  a  lens  and  see 
if  you  can  make  out  what 
they  contain.  These  cups 
are  the  spore  cases.  The 
lichen  fungus  belongs  to 
the  division  of  sac  fungi, 
which  produce  their 
spores  in  closed  sacs,  or 
cups. 

380.  Structure  of  the 
thallus.  —  Make  a  thin 
section  through  a  thallus  and  place  under  the  microscope. 
Notice  the  small  green  bodies  enveloped  in  the  hypha?  of  the 
fungus.  Are  they  most  abundant  near  the  upper  or  the  lower 
epidermis?  Has  their  green  color  anything  to  do  with  this, 
and  with  the  difference  in  color  between  the  two  surfaces  of 
the  thallus  ?     (184.)    Do  they  look  like  chlorophyll  granules  ? 


Fig.  470.  — Portion  of  the  thallus  of  a  lichen, 
magnified,  showing  imprisoned  algai. 


CRYPTOCIAMS  331 

Can  you  tell  what  they  are  ?  Compare  with  your  study  of 
the  unicellular  algae  (337)  and  with  Fig.  429.  Does  this 
throw  any  light  on  their  real  nature? 

381.  The  lichen  thallus  a  composite  body.  —  You  will 
probably  have  no  difficulty  in  making  out  that  these  small 
round  bodies  are  green  alga^  of  some  kind,  but  of  what  species 
will  depend  upon  the  kind  of  lichen  with  which  it  is  associated. 
In  Cladonia  and  the  bearded  lichen  (Fig.  473),  it  is  a  proto- 
coccus  ;  in  other  forms,  a  pleurococcus  or  a  nostoc — and  so 
on,  each  species  of  lichen  fungus  being  specialized  to  a  cer- 
tain form  of  alga.     The  great  botanist,  De  Bary,  showed 


Fig.  471.  —  Artificial  lichen  mycelium,  m,  made  by  sowing  spores  of  a  fungus, 
sp,  among  alga  cells,  a. 

that  it  is  even  possible  to  produce  a  lichen  thallus  artificially 
by  sowing  the  spores  of  a  fungus  among  the  cells  of  the  par- 
ticular alga  with  which  it  is  able  to  unite.  The  spores  will 
germinate  without  the  alga,  but  soon  perish  unless  they  come 
in  contact  with  the  right  one.  It  is  thus  made  clear  that  the 
lichen  plant  as  a  whole  is  a  combination  of  elements  belong- 
ing to  two  distinct  orders,  the  alga?  and  fungi,  but  so  closely 
associated  as  to  constitute  practically  a  single  individual. 


332  PRACTICAL  COURSE   IK  BOTANY 

382.  Slavery,  or  partnership?  —  Now,  what  can  be  the 
object  of  this  pecuUar  association?  Is  it  a  symbiosis,  or 
a  case  of  enslavement?  The  fungi,  as  we  know,  are  all 
parasites,  unable  to  manufacture  their  own  food  or  to  exist 
at  all  except  at  the  expense  of  other  organisms,  living  or  dead. 
But  the  lichens  have  refined  upon  the  gross  rapacity  of  their 
order,  and  instead  of  indiscriminately  destroying  the  hosts 
that  furnish  their  nourishment,  have  used  their  victims  to 
better  purpose  by  converting  them  into  contented,  well-fed 
slaves!  The  imprisoned  algse  perform  for  them  the  same 
service  that  the  chlorophyll  bodies  do  for  the  higher  plants, 
and  so  the  lichen  fungi  have  the  advantage  of  other  parasites 
in  getting  their  food  manufactured  at  home,  so  to  speak. 
And  while  the  algae  have  to  do  double  work  in  order  to  feed 
both  themselves  and  their  masters,  the  fungus,  in  return, 
shelters  them  against  cold  and  drought,  and  prolongs  their 
growing  period  by  giving  them  a  more  continuous  supply 

of  moisture  and  food  materi- 
als, which  it  draws  from  the 
substratum  by  means  of  its 
rhizoids.  In  this  way  both 
plants  are  enabled  to  live  in 
situations  that  neither  could 
occupy  without  the  other. 

383.  Reproduction.  —  The 
multiplication  of  the  lichen 
algae  is  exclusively  vegetative. 
The  fungus,  on  the  other 
hand,  reproduces  normally 
by  spores,  and  the  fruiting 
bodies  found  on  the  thallus 
originate  from  the  fungus 
mycelium. 

384.  Classification. — 
Fig.  472.— a    crustaccous    lichen   To  be  strictly  accuratc,  the 

(Graphis   elegans)    growing   on  holly:   A,  I'l        r  iiii       t 

natural  size ;  B,  slightly  magnified.  tWO  KlUdS  01  Vegetable  DOdieS 


CRYPTOGAMS 


333 


that  make  up  the  lichen  thallus  would  probably  have  to  be 
classified  separately,  as  alga)  or  fungi,  respectively,  but  as 
fructification  is  the  generally  accepted  basis  of  classification, 
and  the  plant  body  is  too  intimately  permeated  with  both 
kinds  of  tissue  to  be  divided,  each  lichen  body  as  a  whole  is 
classed  with  its  particular  kind  of  fungus.  The  entire  group, 
on  account  of  the  distinctive   characters  that  mark  it,  is 


473 

Figs.  473,  474.  —  Fruticose  lichens:     473, 
Cladonia  rangiferina,  reindeer  moss 


Usnea  harhala,  bearded   lichen  ;    474, 
A,  sterile  ;  B,  fruiting  portion. 


placed  in  a  separate  order  of  its  own.  This  includes  three 
principal  divisions,  distributed  according  to  the  shape  of  the 
thallus,  and  its  habit  of  growth  :  (1)  Crustaceous,  those  that 
adhere  closely  to  the  substratum,  as  if  glued  or  inscribed  on 
it ;  (2)  FoUaceous,  with  a  broad,  more  or  less  lobed  and  leaf- 
like thallus  that  adheres  loosely  to  the  substratum  by  means 
of  rhizoids  springing  from  its  under  surface ;  (3)  Fruticose, 
with  branching,  stonilikc  thallus  attached  at  the  base  like  a 
regularly  rooting  plant  (Figs.  473,  474).  Among  these  are 
the  Iceland  moss,  used  as  an  article  of  food  by  man,  and  the 
reindeer  moss  (Cladonia  rangiferina),  which  is  the  chief  sus- 
tenance of  the  reindeer. 


334  PRACTICAL  COURSE  IN   BOTANY 

Practical  Questions 

1.  Have  lichens  any  economic  value  ?     (384.) 

2.  In  what  way  are  they  most  useful?     (320.) 

3.  Do  you  find  them,  as  a  general  thing,  on  healthy  young  trees  and 
boughs,  or  on  old  ones,  and  those  showing  signs  of  decay  ? 

4.  Do  you  ever  find  them  growing  on  trees  or  other  objects  in  densely 
inhabited  areas,  —  cities,  large  towns,  and  manufacturing  centers  ? 

5.  Do  they  grow  more  thickly  on  the  shady  (northern)  side  of  rocks, 
walls,  and  trees  growing  in  the  open,  than  on  the  sunny  and  (presumably) 
warmer  sides  ? 

6.  Mention  some  ways  in  which  a  growth  of  lichens  might  be  beneficial 
to  a  tree. 

7.  In  what  ways  could  it  be  harmful  ? 

V.     LIVERWORTS 

Material.  —  Liverworts  can  generally  oe  found  growing  with  mosses 
in  damp,  shady  places,  and  are  easily  recognized  by  their  flat,  spreading 
habit,  which  gives  them  the  appearance  of  green  lichens.  Marchantia 
polymorpha  (Fig.  475),  one  of  the  largest  and  best  specimens  for  study, 
is  common  in  shady,  damp  ground  throughout  the  states.  It  is  dioecious, 
and  specimens  bearing  both  male  and  female  organs  should  be  provided. 
Lunidaria,  a  smaller  species  that  can  be  recognized  by  the  little  crescent- 
shaped  receptacles  on  some  of  the  divisions  of  the  thallus,  is  abundant 
in  greenhouses  on  the  floor,  or  on  the  sides  of  pots  and  boxes  kept  in  damp 
places ;  but  the  spore-bearing  receptacles  are  seldom  or  never  present, 
the  species  being  an  introduced  one  and  possibly  rendered  sterile  by 
changed  conditions.  Anthoceros  (Fig.  426)  and  leafy  liverworts,  such 
as  that  shown  in  Fig.  484,  also  make  good  examples  for  study. 

Experiment  97.  Why  are  the  upper  and  under  sides  of  a  liver- 
wort DIFFERENT  ?  —  Plant  a  growing  branch  of  marchantia,  or  of  any 
flat,  spreading  liverwort,  in  moist  earth  so  that  the  upper  side  will  lie  next 
the  soil,  and  watch  for  a  week  or  two,  noting  the  changes  that  take  place. 
What  would  you  infer  from  these  as  to  the  cause  of  any  differences  that 
may  have  been  observed  between  the  two  surfaces? 

385.  Examination  of  a  typical  liverwort  —  The  thallus.  — 
The  broad,  flat,  branching  organ  that  forms  the  body  of  the 
plant  is  the  thallus.  Examine  the  end  of  each  branch ; 
what  do  you  find  there?  Are  the  two  forks  into  which  the 
apex  of  the  branches  divides  equal  or  unequal  ?  Compare 
the  growing  end  with  the  distal  one ;   does  it  proceed  from 


CRYPTOGAMS 


335 


a  true  root  ?     Notice  that  as  the  lower  end  dies,  the  growing 
branches  go  on  increasing  and  reproducing  the  thallus. 

Do  you  find  anything  Uke  a  midrib  ?  If  so,  trace  it  through 
the  branches  and  body  of  the  thallus ;  where  does  it  end  ? 
Does  it  seem  to  be  formed  like  the  midrib  of  a  leaf  ?     Hold 


>'■' 


475 


476 


Figs.  475,  476.  —  UmbrolUi  liverwort  (Mnrchnnlia  polymorphn)  :  475,  portion  of  a 
female  thallus  about  natural  size,  showing  dichotomous  branching  ;  /,  /,  archegonial 
or  female  receptacles  ;  r,  rhizoids  ;  476,  portion  of  a  male  thallus  bearing  an  anther- 
idial  disk  or  receptacle,  d,  and  gemmaj,  g,  g. 

a  piece  of  the  thallus  up  to  the  light  and  see  if  you  can  detect 
any  veins.  Is  it  of  the  same  color  in  all  parts,  and  if  there  is 
a  difference,  can  you  give  a  reason  for  it?  Examine  the 
upper  surface  with  a  lens.  Peel  off  a  piece  of  the  epidermis, 
place  it  under  a  low  power  of  the  microscope,  or  between 
two  moistened  bits  of  glass,  and  hold  up  to  the  light,  keeping 
the  upper  surface  toward  you;    what  is  its  appearance? 


336         PRACTICAL  COURSE  IN  BOTANY 

Observe  a  tiny  dot  near  the  center  of  the  rhomboidal  areas 
into  which  the  epidermis  is  divided  and  compare  it  with 
your  drawings  of  stomata  (181,  183). 
What  would  you  judge  that  these  dots 
are  for?  While  differing  in  structure 
from  the  stomata  of  leaves,  they  serve 

Fig.  477. — ^  A  portion     ,,  ,  ,  ,     , 

of  the  upper  epidermis  the  Same  purposes  and  may  be  regarded 
of  marchantia,  magni-   ^s  a  morc  rudimentary  form  of  the  same 

fied,  showing  rhomboidal 

plates  with  a  stoma  in     Organ. 

^^*'^-  386.   Rhizoids.  —  Wash  the  du-t  from 

the  under  side  of  a  thallus  and  examine  with  a  lens ;  how 
does  it  differ  from  the  upper  surface  ?  Do  you  see  anything 
like  roots  ?  Place  one  in  a  drop  of  water  under  the  micro- 
scope. Compare  with  similar  organs  found  on  the  lichen 
(379).  What  are  they?  Would  rhizoids  be  of  any  use  on 
the  upper  side  ?  stomata  on  the  under  side  ? 

387.  Gemmae. —  Look  along  the  upper  surface  for  little 
saucer-shaped  (in  lunularia,  crescent-shaped)  cupules  {g,  g, 
Fig.  476).  Notice  their  shape  and  position,  whether  on  a 
midrib  or  near  the  margin.  Examine  the  contents  with 
a  lens  and  see  if  you  can  tell  what  they  are.  These  little 
bodies,  called  gemmce,  are  of  the  nature  of  buds,  by  which 
the  plant  propagates  itself  vegetatively  somewhat  as  the 
onion  and  the  tiger  lily  do  by  means  of  bulblets.  Sow  some 
of  the  gemma)  on  moist  sand,  cover  them  with  a  tumbler 
to  prevent  evaporation,  and  watch  them  develop  the  thalloid 
structure. 

388.  The  fruiting  receptacles.  —  Procure,  if  possible, 
thalli  with  upright  pedicels  bearing  flattened  enlargements 
at  the  top  (Figs.  475,  476).  These  are  thallus  branches 
modified  into  receptacles  containing  the  reproductive  organs, 
which,  in  marchantia,  are  dioecious,  the  two  kinds  growing 
on  separate  thalli.  Notice  their  difference  in  shape,  one 
kind  being  slightly  lobed  or  scalloped,  the  other  rayed  like 
the  spokes  of  a  wheel.  The  first  kind  are  known  as  antherid- 
ial,  or  male,  receptacles;  the  second  as  aichegonial,  or  female. 


CRYPTOGAMS 


337 


389.  The  antheridia.  —  Examine  one  of  the  male  recep- 
tacles on  both  surfaces  and  in  vertical  section.  Notice  the 
tiny  egg-shaped  bodies  sunk  in  little 
cavities  between  the  lobes  just  under 
the  upper  epidermis  (Fig.  478).  These 
are  antheridia.  When  mature,  they 
rupture  at  the  apex,  and  multitudes  of 
extremely  small  bodies,  called  anthero- 
zoids,  or  spermatozoids,  are  discharged 
from  them, 

390.  Archegonia. — Next  examine  one 
of  the  female  receptacles.  Look  on  the 
under  surface,  between  the  narrow  divi- 
sions of  the  receptacle,  for  radiating  rows     ^^^  473  _  Longitudinal 

of   flask-shaped   bodies   with    their   necks    section  of  a  male  receptacle 

,       ,  -  in  J    J    of  marchantia  polymorpha, 

turned    downward,    and    all    surrounded    magnified:   a,  antheridia; 

by  a  toothed  sheath  or  involucre  (Fig.  <-thaiius;  ..ventral scales; 

•^  ^  r,  rhizoids. 

479).  These  bodies  are  the  archegonia, 
or  female  organs,  and  correspond,  loosely  speaking,  to  the 
ovaries  of  flowering  plants.  If  the  receptacle  is  a  mature 
one,  the  archegonia  will  be  replaced 
by  the  ripe  spore  cases  (sporangia), 
as  at  /,  Fig.  479. 

Make  enlarged  drawings  of  the 
upper  surface  of  a  male  and  a  female 
receptacle,  and  of  a  vertical  section 
of  each,  passing  through  an  anther- 
idium  in  the  male,  and  an  arche- 
gonial  row  in  the  female  receptacle. 
Label  the  parts  observed  in  each. 

391,  Minute  study  of  an  arche- 
gonium.  —  Place  under  the  micro- 
scope a  very  thin,  longitudinal  section 
through  a  ray  of  a  receptacle  con- 
taining a  young  archegonium,  and  observe  that  the  latter 
consists  of  a  lower  portion,  the  venter,  v,  Fig.  480,  and  an 


Fig.  479.  —  Under  side  of  an 
archegonial  receptacle  enlarged. 
The  archegonia  are  borne 
among  the  hairs  on  the  under 
surface,  which  is  presented  to 
view  in  the  figure  ;  /,  a  spore 
case. 


338 


PRACTICAL  COURSE  IN  BOTANY 


upper  part,  the  neck,  which  is  perforated  by  the  neck  canal, 
ca.  The  venter  contains  the  egg  cell,  o,  and  the  ventral  canal 
cell,  vc.  The  neck  canal  is  filled  with  small  cells  which, 
at  maturity,  dissolve  into  a  mucilaginous  substance  that 
swells  on  being  wet  and  discharges  itself  through  the  top 
of  the  neck,  leaving  an  open  passage  to  the  venter,  where 
the  egg  cell  is  ready  to  be  ferti- 
lized. 

Make  a  drawing  of  the  section  as 
seen  under  the  microscope,  labeling 
all  the  parts. 

392.  Fertilization.  —  In  the  liver- 
worts, and  in  cryptogams  generally, 
this  process  has  to  take  place  under 
water,  as  the  antherozoids  are  motile 
only  in  a  liquid,  but  the  amount  re- 
quired is  so  small  that  a  few  drops 
of  rain  or  dew  will  enable  them  to 
make  their  journey  to  the  archego- 
nium.  The  mucilaginous  substances 
discharged  from  the  neck  canal  at- 
tract them  to  the  mouth  of  the  open- 
FiGs.  480,  481.— 480,  young  iug,  ouc  or  more  of  them  penetrates 

archegonium  of    M    polymor-  ^     ^j^               ^   j^       ^^^  fertilization  is  aC- 

pha ;  V,  ventral  portion ;  o,  egg  _  °='          ' 

cell ;  vc,  ventral  canal  and  cells  ;  COmplished.       Do   yOU   SCe   any  aual- 

ca,  neck  canal  with  cells;  481,  •         1      1                  it  •              1     ±1 

the  same  ready  for  fertilization  Ogl^S    bctween     thlS     and     the     Same 

after  discharge  of  the  mucilagi-  function     amOUg     floWCring    plauts? 

nous  fluid.  /^_^    ^^^   s 

(250,  251.) 
393 .  The  spore  case.  —  After  fertilization  the  egg  becomes 
an  oospore,  capable  of  producing  a  new  plant.  Instead, 
however,  of  separating  from  the  mother  plant  and  giving 
rise  to  an  independent  growth,  it  germinates  within  the  ar- 
chegonium and  produces  there  a  small,  stalked  body,  called 
a  sporogonium,  or  sporophyte,  which  at  length  ripens  into 
a  spore  case,  as  shown  at  /,  Fig.  479.  At  maturity  this 
capsule-like  sporophyte  ruptures  at  the  apex,  and  discharges 


CRYPTOGAMS  339 

a  mass  of  spores,  mingled  with  elongated  filaments  called 
elators,  which,  by  their  elastic  movements,  assist  in  dissem- 
inating the  spores.  These  latter,  on  germinating,  produce, 
not  a  simple  sporophyte  like  that  which  bore  them,  but 
the  thallus  of  the  liverwort  with  all  its  complicated  arrange- 
ment of  antheridia  and  archegonia  and  vegetative  organs 
that  seem  to  foreshadow,  by  the  analogies  they  suggest, 
the  coming  of  the  higher  plants. 

394.  Sexual  and  asexual  reproduction.  —  We  find  here 
a  very  marked  change  from  the  simple  reproductive  processes 
observed  in  the  algae  and  fungi.  In  the  forms  thus  far  con- 
sidered, this  function  was  carried  on  mainly  by  simple  vege- 
tative fission  or  budding,  with  a  more  or  less  irregular  in- 
tervention of  resting  spores.  If  only  one  kind  of  spore  is 
concerned,  reproduction  is  said  to  be  asexual.  When  two 
different  kinds  of  cells,  the  egg  and  sperm  cell,  unite  to  form 
an  oospore,  as  in  the  liverworts,  reproduction  is  said  to  be 
sexual.  Wliile  sexual  reproduction  takes  place  to  some 
extent  among  both  algae  and  fungi,  the  prevailing  method 
among  thallophytes  is  asexual,  and  may  be  carried  on  in 
three  different  ways :  by  fission  (and  budding),  by  resting 
spores,  and  by  conjugation. 

Representing  the  plant  body  by  A  and  the  resting  spores 
by  a,  the  primitive  asexual  processes  may  be  expressed  to 
the  eye  by  the  accompanying  formulas  :  — 

(1)  Fission  and  budding :    A->A-^A-^A->- 

(2)  Resting  spores  :   Aa—>Aa-^Aa—> 

(3)  Conjugation:  A  4- A->a— >A  +  A->a-> 

In  (3),  as  was  seen  in  the  conjugating  cells  of  the  spirogyra 
(342),  the  method  is  a  little  more  complicated,  showing  an 
approach  toward  the  sexual  process.  In  each  of  these  cases, 
however,  there  is  only  one  kind  of  cell  concerned,  while  in 
the  liverworts  there  are  not  only  different  kinds,  techni- 
cally known  as  gametes,  but  specialized  organs,  archegonia 
and  antheridia,  for  producing  them.  The  thallus  body 
bearing  these  organs  is  termed  the  gatnetophyie,  because  ifc 


340  PRACTICAL  COURSE  IN  BOTANY 

bears  the  gametes,  or  sexual  organs,  —  the  suffix  phyte  mean- 
ing a  plant ;  for  example,  epiphyte,  on  or  upon  plants  ;  spermo- 
phyte,  or  spermatophyte,  seed  plant ;  sporophyte,  spore  plant. 
The  sporophyte,  produced  within  the  archegonium,  bears 
simple  nonsexual  spores  that  are  capable  of  germinating 
independently.  Structurally  it  is  a  separate,  individual 
organism,  though  it  does  not  appear  as  such  in  this  class, 
but  lives  inclosed  in  the  archegonium,  as  a  parasite  on  the 
mother  plant. 

395.  Alternation  of  generations.  —  If  we  represent  the 
sporophyte  by  >S^,  the  thallus,  or  gametophyte,  by  G,  the 
female  gamete,  or  egg  cell,  by  fg,  the  antherozoids  (male 
gametes)  by  7ng,  the  fertilized  egg  cell,  or  oospore,  result- 
ing from  their  union  by  oos,  and  the  asexual  spores  dis- 
charged from  the  sporophyte  by  0,  this  complicated  mode 
of  reproduction  may  be  expressed  diagrammatically  as 
follows :  — 

'^<C  ^>ods-*  S ».  0 ^(^^<r  ">  oos  -^S  — >  0 vG^etc. 

A  glance  at  the  diagram  will  show  a  continual  inter- 
change of  the  sexual  and  asexual  modes  of  reproduction,  in 
which  each  generation  gives  rise  to  its  opposite,  the  asexual 
sporophyte  producing  the  sexual  gametophyte,  and  this  in 
turn,  through  its  gametes,  giving  rise  to  the  asexual  sporo- 
phyte. This  regular  recurrence  in  genealogical  succession  of 
two  differing  forms  is  what  is  meant  by  the  expression  "  alter- 
nation of  generations."  Analogous  processes  occur  also 
among  some  of  the  thallophytes,  but  as  there  is  no  well- 
defined  differentiation  of  sporophyte  and  gametophyte, 
alternation  proper  may  be  regarded  as  beginning  with  the 
bryophytes.  The  subject  is  a  complicated  one  and  some- 
what difficult  to  grasp,  but  it  is  important  to  form  a  correct 
idea  of  it  and  to  fix  clearly  in  mind  the  different  modes  of 
reproduction  as  we  proceed  from  the  lower  to  the  higher  forms 
of  vegetation,  since  in  this  way  alone  can  their  biological 


CRYPTOGAMS  341 

relationships  and  their  order  of  succession  in  the  evolutionary 
scale  be  made  intelligil)le. 

VI.     MOSSES 

Material.  —  One  of  the  most  widely  distributed  of  mosses  is  the 
Sphagnum,  or  peat  moss,  so  generally  used  by  florists  in  packing  plants  for 
shipment,  and  it  can  be  obtained  from  them  at  almost  all  times.  It  is 
rather  difficult,  however,  to  find  spechnens  with  the  fruiting  organs,  since 
they  are  rarely  to  be  met  with  except  in  late  autumn  or  early  spring. 
Other  common  forms  are  Polytrichum,  Funarin,  and  Mmutn,  any  of  which 
will  meet  all  essential  conditions  of  the  study  outlined  in  the  text. 

396.  The  protonema  or  thallus  stage.  —  In  mosses  the 
sexual,  or  gametophyte  generation  differs  from  that  of 
liverworts  in  undergoing  two  phases.  The  germinating 
cells  of  the  sporophyte  do  not  develop  immediately  into 
the  leafy  stem,  which  is  the  typical  gametophyte  of  true 
mosses,  but  produce  first  a  filamentous,  creeping  structure 


Figs.  482,  483. — Protonoma  of  a  moss:  482,  germinating  spore;  483,  protonema; 


kn,  buds  ;  r,  rhizoids  ;  s,  spore. 

called  the  protonema  (Fig.  483),  that  spreads  over  the 
ground  and  forms  the  tangled  green  felt  usually  observed 
where  mosses  are  growing.  Place  a  few  of  these  filaments  on 
a  slide  in  water,  and  examine  under  the  microscope.  Do 
they  remind  you  of  any  of  the  forms  of  alga3?     Look  near 


342 


PRACTICAL  COURSE  IN  BOTANY 


the  base  of  the  branches  for  knots  or  enlargements,  like 
those  seen  at  kn,  Fig.  483.  These  are  buds  from  which  the 
leafy  moss  stems  will  develop.  Do  they  correspond  to  any- 
thing observed  among  the  thallophytes  ?  Notice  the  rootlike 
filaments  that  extend  under  ground ;  how  do  they  differ  from 
the  ones  above  ground?  Why  are  they  colorless?  How 
do  you  know  that  they  are  not  true  roots?  [67  (a),  379.] 
Sketch  one  of  each  kind  of  filament  sufficiently  enlarged  to 
show  the  cells  composing  it. 

A  protonema  that  arises  directly  from  the  spore  is  said 
to  be  frimary,  while  those  which  sometimes  spring  from 
rhizoids  above  ground,  or  from  stems  or  leaves,  are 
secondary.  The  fact  that  a  protonema  can  bud  from  parts 
of  the  fruiting  stems  shows  that  the  two  do  not  belong  to 
different  generations,  but  are  merely  successive  stages  of 
a  single  generation,  and  both  together  compose  the  game- 
tophyte. 

397.  The  leafy  stage.  —  In  their  fully  developed  state 
the  true  mosses  show  a  marked  advance  in  organization  over 

the  liverworts.  There  is  a  distinct 
differentiation  of  the  growing  axis  into 
stem  and  leaves,  though  no  true  roots 
are  formed.  The  leaves  are  arranged 
spirally,  on  upright  stems,  while  in  the 
liverworts  the  vegetative  body  is 
either  a  flat,  spreading  thallus,  or  the 
leaves  are  arranged  horizontally  on 
opposite  sides  of  a  prostrate,  or  more 
or  less  inclined,  axis.  Sometimes  a 
second  set  occurs,  on  the  upper  side 
of  the  axis,  but  in  this  case  the  leaves 
are  usually  much  smaller  and  inclined 
to  the  horizontal  arrangement,  as 
shown  in  Fig.  484. 

398.  The  reproductive  organs.  —  The  antheridia  and 
archegonia  are  borne  in  groups  at  the  end  either  of  the  main 


Fig.  484.  —  Scapania,  a 
liverwort  with  leafy  thallus,  ap- 
proaching the  form  of  mosses 
and  lycopodiums.  (From  Coul- 
ter's "Plant  Structures.") 


CRYPTOGAMS 


343 


Fig.  485.  —  Fruiting  recep- 
tacle of  a  moss  {Phascum  cus- 
pidatum),  bearing  botii  anther- 
idia,  an,  and  archegonia,  ar,  at 
the  bifurcated  apex  ;  b,  leaves  ; 
p,  paraphyses. 


axes,  or  of  lateral  branches  (Figs.  485,  486),  but  as  a  rule 
only  one  arch(^goniuin  is  fertilized,   so  the  mature   sporo- 

gonia  are  solitary.     The  plants  may 

be  either  dioecious  or  monoecious,  as 

in  Fig.  485 ;  and  in  )^  ,/ 

the  latter  case,  the 

reproductive  organs 

may  be  borne  on  the 

same,  or  on  different, 

receptacles.     The 

antheridia  and  the 

archegonia  are  both 

mixed   with    club- 
shaped  hairs  called 

paraphyses     (Fig. 

485). 
399.  The  sporophyte.  —  An  examination 
of  the  fruiting  capsule  of  any  of  the  true 
mosses  will  show  that  it  consists  of  a  long 
footstalk,  the  seta,  s,  Fig.  486,  bearing  a 
capsule,  or  ripened  sporogonium,  /,  which 
is  at  first  surmounted  by  a  cap  or  hood, 
known  as  the  calyptra,  c.  The  hood  repre- 
sents the  excessively  developed  and  often 
highly  specialized  wall  of  the  archegonium. 
It  falls  away  at  maturity,  and  the  spores  are 
discharged  through  an  opening  made  by  the 
removal  of  the  operculum,  or  lid,  d.  The 
spores  and  the  capsule  are  both  developed 
from  the  fertilized  egg  (oospore) ,  within  the  suics :  «,  seta,  or  foot- 

1  •  •  1     1 1  •       stalk ;  c,  capsule  with 

archegonmm,  m  much  the  same  manner  as  m  ^..^lypir^ .  f,  capsule 
the  liverworts,  and  together  constitute  the  -if*''''  t'^'^  calyptra  has 

,       ,  ,  i-  Ti  fallen  awav  ;  d,  opor- 

sporophyte,  or  asexual  generation.     It  never  cuium,  or  lid. 
leads  a  completely  independent   existence,  but   remains  a 
partial  parasite  on  the  mother  plant,  though  the  lower  part 
of  the  young  sporogonium  is  usually  provided  with  stomata 


FKi.4SG.  — Fruit- 
ing stem  of  a  mos3 
(Fvlytrichum  com- 
mune) with  ripe  cap- 


344  PRACTICAL  COURSE   IN  BOTANY 

and  chlorophyll  so  that  it  is  capable  of  manufacturing  food. 
In  this  respect  it  shows  a  distinct  advance  on  the  correspond- 
ing phase  of  the  liverworts  —  if  we  except  the  single  genus 
Anthoceros,  which  alone  among  the  liverworts  has  the  cells 
of  the  sporogonium  i)r()vided  with  chlorophyll. 

400.  Alternation  of  generations.  —  The  process  of  repro- 
duction in  mosses  is  so  closely  similar  to  that  of  liverworts 
that  it  is  unnecessary  to  repeat  the  details.  There  are 
some  minor  variations,  but  in  all  essentials  the  processes 
are  the  same  and  may  be  represented  to  the  eye  by  the 
same  formula. 

401.  Relative  position  of  mosses  and  liverworts  in  the 
line  of  evolution.  —  Though  mosses,  as  a  rule,  show  a  higher 
degree  of  organization  than  liverworts,  in  both  generations, 
their  development  has  been  away  from  the  general  course 
of  evolution  followed  by  the  higher  plants.  This,  as  will 
be  seen  later,  tends  towards  a  decreasing  complexity  of 
the  gametophyte  with  increasing  complexity  of  the  sporo- 
phyte,  while  the  mosses  show  increasing  complexity  of  both. 
Like  the  order  of  birds  in  the  animal  kingdom,  they  form 
a  highly  specialized  and  somewhat  isolated  group.  AMiile 
they  may  be  regarded  as  descendants  from  a  common  an- 
cestral stock  with  the  ferns  and  club  mosses,  they  have 
been  switched  off,  so  to  speak,  on  a  side  track  of  the  great 
evolutionary  trunk  line,  and  their  advance  on  this  side 
track  has  carried  them  to  a  point  more  remote  from  the 
course  along  which  the  higher  forms  of  plant  life  have 
traveled  than  the  distant  junction  at  which  they  branched 
off  from  their  less  progressive  kindred,  the  humble  liver- 
worts. 

VII.     FERN  PLANTS 

Material.  —  Any  kind  of  fern  in  the  fruiting  stage.  Several  different 
varieties  should  be  cultivated  in  the  schoolroom  for  observation.  While 
gathering  specimens,  look  along  the  ground  under  the  fronds,  or  in  green- 
houses where  ferns  are  cultivated,  among  the  pots  and  on  the  floor,  for 
a  small,  heart-shaped  body  like  that  represented  in  Figs.  501,  502,  called 
a  prothallium.    It  is  found  only  in  moist  and  shady  places,  and  care  should 


CRYPTOGAMS 


345 


be  taken  in  collecting  specimens,  as  in  their  early  stages  the  prothallia 
bear  a  strong  resemblance  to  certain  liverworts  found  in  the  same  situa- 
tions. The  best  way  is  for  each  class  to  raise  its  own  specimens  by  scat- 
tering the  spores  of  a  fern  in  a  glass  jar,  on  the  bottom  of  which  is  a  bed 
of  moist  sand  or  blotting  paper.  Cover  the  jar  loosely  with  a  sheet  of 
glass  and  keep  it  moist  and  warm,  and  not  in  too  bright  a  light.  Spores 
of  the  sensitive  ferns  {Onoclea)  will  germinate  in  from  two  to  ten  days, 
according  to  the  temperature.  Those  of  the  royal  fern  {Osmunda)  ger- 
minate promptly  if  sown  as  soon  as  ripe,  but  if  kept  even  for  a  few  weeks 
are  apt  to  lose  their  vitality.  The  spores  of  sensitive  fern  can  be  kept 
for  six  months  or  longer,  while  those  of  the  bracken  (Pteris)  and  various 
other  species  require  a  rest  before  germinating,  so  that  in  these  cases  it 
is  better  to  use  spores  of  the  previous  season. 

402.  Study  of  a  typical  fern.  —  Observe  the  size  and 
general  outline  of  the  fronds,  and  note  whether  those  of 
the  same  plant  are  all  alike,  or  if  they  differ  in  any  way, 
and   how.     Observe   the 

shape  and  texture  of  the     "^  "'"^^         - -^   ^  ^     ^.u   -, 

divisions  or  pinnae  com- 
posing the  frond,  their, 
mode  of  attachment  to 
the  rachis,  and  whether 
they  are  simple,  or 
notched,  or  branched  in 
any  way.  Hold  a  pinna 
up  to  the  light  and  notice 
the  veining.  Is  it  like  any 
of  the  kinds  described  in 
171,  172?  In  what  re- 
spect is  it  different? 
This  forked  venation  is 
a  very  general  character- 
istic of  ferns.  When  the 
forks  do  not  reticulate  or 
intercross,  the  veins  are       Figs.  487-491.— a  fom  plant:  487,  fronds 

*rl   +       K      -f  •  fVi  ^"*^  rootstock;    488,  fertile   pinna:    s,  s,  sori ; 

Saia  to    De  tree  ;    are  iney  4^9   pr^sg  section  of  a  stipe,  showing  ends  of  the 

free  in  VOUr  specimen    or  fil5rovaseularhundles;490,aelusterofsporanKia, 

,  -       T\/r     1      '  maKnifi(Hl  ;  491,  a  single  sporangium  still  more 

reticulated:       Make      a  maguified,  shedding  its  spores. 


346  PRACTICAL  COURSE   IN  BOTANY 

sketch,  labeling  the  primary  branches  of  the  frond,  pinnce 
(sing.,  pinna),  the  secondary  ones,  if  any,  pinnules,  and  the 
common  stalk  that  supports  them,  stipe.  Note  the  color, 
texture,  and  surface  of  the  stipe.  If  any  appendages  are 
present,  such  as  hairs,  chaff,  or  scales  (in  Pteris,  nectar 
glands),  notice  whether  they  are  equally  distributed.  If  not, 
where  are  they  most  abundant  ? 

Examine  the  mode  of  attachment  of  the  stipes  to  their 
underground  axis.  Break  one  away  and  examine  the  scar. 
Compare  with  your  drawings  of  leaf  scars  and  with  Fig. 
105.  Do  the  stipes  grow  from  a  root  or  a  rhizome?  How 
do  you  know?  Do  you  find  any  remains  of  leafstalks  of 
previous  years?  How  does  the  rootstock  increase  in 
length?  Measure  some  of  the  internodes;  how  much  did 
it  increase  each  year?  Cut  a  cross  section  and  look  for 
the  ends  of  the  fibrovascular  bundles.  Trace  their  course 
through  several  internodes.  Do  they  run  straight,  or  do 
they  turn  or  bend  in  any  way  at  the  nodes?  If  so,  where 
do  they  go?  Do  you  see  anything  like  roots?  Where  do 
they  originate  ?  Put  one  of  them  under  the  microscope  and 
find  out  whether  they  are  roots  or  hairs. 

True  roots  are  first  developed  in  the  pteridophytes.  Since 
those  of  the  fern  spring  from  an  underground  stem,  to  what 
class  of  roots  do  they  belong  ?     (83.) 

403.  Minute  study  of  a  fern  stem.  —  Place  a  very  thin 
section  of  a  fern  rhizoma,  or  of  the  stipe  of  a  frond,  under 
the  microscope.  Except  in  very  young  stems  the  vascular 
bundles  are  arranged  in  a  ring,  or  sometimes  in  two  or 
more  rings  (Fig.  492),  with  plates  of  strengthening  tissue, 
I,  I,  between  the  inner  and  outer  rings.  Notice  the  inner 
epidermal  layer  of  hard  brown  tissue,  and  within  that,  the 
soft  parenchyma,  which  fills  the  rest  of  the  interior.  Test 
it  with  iodine  and  observe  how  rich  in  starch  it  is.  If  the 
section  of  a  petiole  is  under  observation,  the  details  will 
be  somewhat  different ;  would  you  expect  to  find  as  much 
starch  in  the  stipe  as  in  the  rootstock  ?    Why,  or  why  not  ? 


CRYPTOGAMS 


347 


Make  a  longitudinal 
section  of  a  rhizome 
through  the  point 
where  a  leafstalk  is 
attached  and  trace  the 
course  of  the  bundles. 
This  will  be  facilitated 
if  the  specimen  has 
stood  in  eosin  solution 
a  few  hours.  Make 
enlarged   drawings   of 

both  sections,  labeling  Fig.  492.  —  Diagram  of  a  cross  section  through 

oil    +V>o   r»Qr-i-G  *^*^  ^*^™   °^  ^  ^®''"  (P^f^i^)'  «.  «.  «•  "ngs  of  fibro- 

au  lae  pans.            ^  vascvdar  bundles ;  Z,Z,  plates  of  strengthening  tissue, 

Clearly  differentiated  with  a  ring  of  flbrovascular  bundles  between  them  ; 

,       , .            ,            n  Ip,    zone    of    strengthening   fibers ;   r,  cortex ;  e, 

conducting    bundles  epidermis. 
occur   in   the   mosses, 

but  they  are  of  much  simpler  structure  than  in  the  pterido- 
phytes,  consisting  usually  of  a  single  central  strand,  and  are 
found  more  frequently  in  the  leaves 
than  in  the  stems.  A  true  vascular 
structure  appears  first  in  the  pteri- 
dophytes,  whence  these  plants  are 
distinguished  as  vascular  cryptogams. 
404.  Fructification.  —  Examine 
the  back  of  a  fruiting  frond;  what 
do  you  find  there  ?  These  dots  are 
the  sori  (sing.,  sorus),  or  spore  clus- 
ters, and  the  fronds  or  pinnae  bear- 
ing them  are  said  to  be  fertile.  Are 
there  any  differences  of  size,  shape, 
etc.,  between  the  fertile  and  the 
sterile  fronds  of  your  specimen? 
between  the  fertile  and  the  sterile  pinnsB?  On  what  part 
of  the  frond  are  the  fertile  pinnae  borne  ?  Notice  the  shape 
and  position  of  the  sori,  and  their  relation  to  the  veins, 
whether  borne  at  the  tips,  in  the  forks,  on  the  upper  side  t 


493 


494 


Figs.  493-494.  —  P  a  r  t  s  of 
fertile  pi^inae :  493,  of  polypo- 
dium,  ei^larged,  showing  the  sori 
without  indusium  ;  494,  of  pellea, 
showing  indusium  formed  by  tho 
revolute  margin. 


348 


PRACTICAL  COURSE  IN  BOTANY 


495  490 

Figs.  495-496.  —  Christmas  fern  (As- 
pidium) :  495,  part  of  a  fertile  frond,  natural 
size  ;  496,  a  pinna  enlarged,  showing  the 
sori  confluent  under  the  peltate  indusia. 


(toward  the  margin),  or  the  lower  (toward  the  midrib). 
Look  for  a  delicate  membrane  iindusium)  covering  the  sori, 
and  observe  its  shape  and  mode  of  attachment.     If  the 

specimen  under  examination 
is  a  polypodium,  there  will  be 
no  indusium;  if  a  maiden- 
hair, or  a  bracken,  it  will  be 
formed  of  the  re  volute  mar- 
gin of  the  pinna.  In  lady 
fern  and  Christmas  fern  {As- 
indium),  the  sori  frequently 
become  confluent,  that  is,  so 
close  together  as  to  appear 
like  a  solid  mass.  Sketch  a 
fertile  pinna  as  it  appears  under  the  lens,  bringing  out  all 
the  points  noted. 

405.  The  spore  cases.  —  Look  under  the  indusium  at 
the  cluster  of  little  stalked  circular  appendages  (Fig.  490). 
These  are  the  sporangia,  or  spore  cases,  in  which  the  re- 
productive bodies  are  borne.  Place  one  of  them  under  the 
microscope,  and  it  will  be  found  to  consist  of  a  little  stalked 
circular  body  like  a  tennis  racket  (Fig.  491),  surrounded 
by  a  jointed  ring 
called  the  an- 
nulus.  Watch  a 
few  moments  and 
see  if  you  can 
find  out  the  use 
of  the  annulus. 
If  not,  warm  the 
slide  and  you  will  probably  see  the  ring  straighten  itself 
with  a  sudden  jerk,  rupturing  the  wall  of  the  sporangium 
and  discharging  the  spores  with  considerable  force.  If  this 
does  not  happen,  add  a  drop  of  strong  glycerine  to  a  speci- 
men mounted  in  water ;  the  rupture  will  be  apt  to  follow 
quickly.    What  causes  it,  in  either  case?    [56,  (1);  Exp.  19.] 


497 


498 


499 


500 


Figs.  497-500.  —  Spores  of  pteridophytes,  magnified : 
497,  a  fern  spore  ;  498,  499,  two  %aews  of  a  spore  of  a  club 
moss  ;  500,  spore  of  a  common  horsetail  (Equisetum  arveuse) . 


CRYPTOGAMS 


349 


406.  The  sporophyte.  —  The  spores  found  in  such  abun- 
dance on  the  fertile  pinna;  are  all  alike,  and  each  one  is 
capable  of  germinating  and  continuing  the  work  of  reproduc- 
tion as  effectually  as  the  sexual  spores  of  the  bryophytes. 
The  fertile  frond,  or  part  of  a  frond,  on  which  they  are  borne 
is  called  a  sporophyll  (spore-bearing  leaf),  and  the  entire 
plant  is  the  sporophyte,  which,  with  its  crop  of  spores,  makes 
up  one  generation. 

It  is  important  to  observe  that  in  the  ferns  and  in  all  pteri- 
dophytes  the  sporophyte  is  the  conspicuous  and  highly 
organized  body  that  is  commonly  recognized  as  the  normal 
growing  plant;  while  with  the  bryophytes  just  the  reverse 
holds  true,  —  the  sexual  generation,  or  gametophyte,  repre- 
sents the  normal  plant  structure,  while  the  sporophyte  is 
an  insignificant  appendage 
which  never  attains  an 
independent  existence. 
Broadly  speaking,  in  bryo- 
phytes, it  is  a  spore  fruit ; 
in  the  pteridophytes  and 
spermatophytes  a  highly 
developed  plant. 

407.  The  gametophyte. 
—  When  one  of  these  asex- 
ual spores  germinates,  it 
produces,  not  a  fern  plant 
like  the  one  that  bore  it, 
but  a  small,  heart-shaped 
body  like  that  shown  in  Fig.  501.  Examine  one  of  these  bod- 
ies carefully  with  a  lens.  Observe  that  there  are  no  veins  nor 
fibrovascular  bundles,  and  the  whole  body  of  the  plant  seems 
to  consist  of  one  uniform  tissue.  Compare  it  with  the  forked 
apex  of  a  branching  thallus  of  a  liverwort.  Do  j^ou  perceive 
any  points  of  similarity  ?  The  two  are,  in  fact,  morphologi- 
cally the  same.  This  heart-shaped  body  is  called  a  prothal- 
lium,  and  is  the  gametophyte  of  the  fern.     It  may  be  of 


501 


502 


Figs.  501, 502.  —  Prothallium  of  a  common 
fern  (Aspidium):  501,  under  surface,  showing 
rhizoids,  rh,  antheridia,  an,  and  archegonia, 
ar ;  502,  under  surface  of  an  older  gameto- 
phyte, showing  rhizoids,  rh,  young  sporo- 
phyte, with  root,  w,  and  leaf,  b. 


350        PRACTICAL  COURSE  IN  BOTANY 

different  shapes,  and  in  some  species  is  branching  and  filamen- 
tous, like  the  protonema  of  a  moss.  Generally,  however,  it 
is  flat  and  more  or  less  two-lobed,  as  shown  in  Fig.  501.  It 
is  small  and  inconspicuous  and  very  short-lived,  being  of 
importance  only  in  connection  with  the  work  of  reproduction. 
Look  with  your  lens  for  a  cluster  of  small,  bottle-shaped 
bodies  just  below  the  deep  cleft  in  the  heart.  If  you  can- 
not make  out  what  they  are,  put  a  thin  section  through 
a  part  of  the  prothallium  containing  one  under  the  micro- 
scope, and  you  will  see  that  they  are  the  archegonia.  Lower 
down  among  the  rhizoids,  near  the  pointed  base,  will  be 
found  the  antheridia.  In  some  species  the  prothalli  are 
dioecious,  one  kind  bearing  antheridia,  the  other  archegonia, 
but  this  is  rare  among  the  true  ferns. 

408.  Fertilization.  —  This  process  is  the  same  in  all  essen- 
tials as  in  the  bryophytes.     As  in  other  cryptogams,  it  can 

take  place  only  under 
K  water,  —  a  circumstance 
which  points  to  an  aquatic 
origin  for  this  subkingdom, 
.-^'  and  through  them  to  the 
entire  flora  of  the  globe. 
The  archegonia  differ 
somewhat  in  shape  from 
those  of  the  liverworts  and 
mosses,  but  a  section  under 
the  microscope  will  show 
that  they  consist  of  essen- 

FiG.503.-Youngarchegoniumofafern.  tially  the  SamC  parts.^  On 
magnified:  K,  neck  canal  cell ;  K',  ventral  aCCOUUt  of  the  similarity  of 
canal  cell :  O,  egg  cell.  . ,  . ,  ,      -  ^ 

these  organs,  the  pterido- 
phytes  and  bryophytes  are  often  classed  together  as  Arche- 
goniates. 

409.  Alternation  of  generations.  —  Among  the  section  of 
ferns  that  we  have  been  considering,  the  order  of  alternation 
corresponds  in  all  essentials  to  that  prevailing  among  the 


CRYPTOGAMS 


351 


bryophytes,  and  may  be  represented  by  the  same  formula. 
The  chief  difference  is  in  the  relatively  much  greater  im- 
portance of  the  sporophyte,  which  may  be  expressed  by 
putting  it  first :  — 

S—^o—^G<^        J>o6a—>S-^o^G<^         N  oos—>S-^o—>G  etc. 
^mg  mg 

But  some  of  the  pteridophytes  —  of  which  the  Selaginella 
offers  a  conspicuous  example  —  have   differentiated   their 


34  507  508 

;.  —  A  kind  of  pteridophyte  (Selaginella  martensii)  with  its  organs  of 

(4,  a  fruiting  branoh  ;  505,  a  microsporophyll  with  a  microsporan- 

icTospores  through  a  rupture  in  tho  wall  ;  500,  a  mogasporophyll 

"anirium :   507.  megasDores :   508,  microspores.     (From  Coulter's 


Figs.  504-508. 

fructification:  504,  ._  

gium,  showing  microspores  through  a  rupture  in  the  wall;  50f 
with  a  megasporangium ;  507,  megaspores ;  508,  microspores. 
"  Plant  structures.") 


352        PRACTICAL  COURSE  IN  BOTANY 

asexual  spores  (o  of  the  formula)  into  two  kinds,  large  and 
small,  known  respectively  as  megaspores  and  microspores. 
The  prothallia  developed  by  the  former  bear  archegonia 
containing  female  gametes  only;  those  by  the  latter,  antheri- 
dia  containing  male  gametes  —  while  in  the  dioecious  bryo- 
phytes,  the  archegonial  and  antheridial  thalli  are  produced 
by  spores  of  the  same  kind. 

The  differentiation  of  the  asexual  spores  in  the  higher 
pteridophytes  gives  rise  to  corresponding  changes  in  the 
sporangia  that  bear  them,  and  even  in  the  sporophylls  them- 
selves, one  kind  bearing  microsporangia  only,  the  other 
megasporangia.  In  this  way  the  differentiation  of  sex  is 
pushed  back,  step  by  step,  until  it  virtually  begins  with  the 
sporophyte,  or  asexual  generation. 

Using  the  same  terms  as  before,  and  representing  the  mi- 
crospores by  the  abbreviation  mo,  the  megaspores  by  Mo, 
the  archegonial  gametophyte  by  arG,  the  antheridial  by 
anG,  the  formula  may  be  modified  to  express  this  more  com- 
plicated process  of  alternation,  as  follows  :  — 

jlo  — >  arG  — >  fg^  y  Mo  —^.arG—^  fg^ 

N  oo.s->5<^  y  ods->Seisc. 

t — >anG — >  mg'^  ^  mo — i-anG — >mg'^ 

Comparing  this  formula  v  ith  the  preceding,  it  will  be  seen 
that  the  increased  complexity  affects  the  sporophyte  at  the 
expense  of  the  gametophy t< ;,  which  has  now  become  a  mere 
dependent  on  the  former. 

410.  Advantages  of  alternation.  —  This  roundabout  mode 
of  reproduction  would  hardly  have  been  developed  unless  it 
had  been  of  some  benefit  to  the  plants  in  which  it  occurs. 
Thc"  chief  advantage  seems  to  be  in  more  rapid  multiplication 
and  consequently  better  chance  to  propagate  the  species,  as 
compared  with  the  slow  process  of  sexual  reproduction  were 
the  plant  confined  to  that  method  alone.  Only  one  plant  is 
produced  by  each  oospore,  and  if  this  were  a  gametophyte 
with  its  limited  number  of  archegonia,  multiplication  would 


CRYPTOGAMS 


353 


be  slow ;  but  the  sporophyte  with  its  millions  of  spores,  each 
capable  of  producing  a  new  individual,  enables  the  species  to 
multiply  indefinitely.  At  the  same  time  the  interposition  of 
a  gametophyte,  or  sexual  generation,  secures  the  introduc- 
tion of  a  new  strain  with  effects  analogous  to  those  of  cross 
fertilization. 

411.  Classification  of  pteridophytes.  —  In  our  study  of 
this  group,  the  ferns  have  been  taken  as  the  type  because 
they  are  the  most  familiar  and  most  widely 
distributed  of  all  the  vascular  cryptogams. 
But  while  they  exceed  in  numbers,  both  of 
individuals  and  species,  all  the  other  orders 
combined,  they  form  only  one  division  of  three 
great  groups  that  make  up  the  class  Pterido- 
phyta.  These  groups  are :  (1)  ferns,  under 
which  are  included,  besides  the  true  ferns,  two 
widely  differing  orders,  with  the  grape  ferns 
and  adder's-tongue  in  one,  and  the  water  ferns 
in  the  other ;  (2)  the  club  mosses,  embracing 
the  two  subdivisions  of  Lycopodium  and  Sel- 
aginella;  (3)  the  horsetail  family,  including 
horsetails  c^nd  scouring  rushes.  Orders  (2) 
and  (3)  are  grouped  together  as  cone-bearing 
(strobilaceous)  pteridophytes,  because  their 
sporangia  are  clustered  in  oblong  heads,  or 
strobiles  (Fig.  509),  somewhat  like  the  cones  of 
the  pine.  The  orders  of  pteridophytes  differ 
greatly  among  themselves,  but  agree  in  pos- 
sessing certain  characteristics  that  point  to 
their  derivation  from  a  common  ancestry. 

412.  Distinction  between  pteridophytes  and 
bryophytes.  —  In  passing  from  the  Thallo- 
phytes  and  Bryophytes  to  the  vascular  cryptogams,  we  cross 
the  widest  chasm  in  the  vegetable  kingdom  —  a  gap  relatively 
as  great  as  that  between  vertebrates  and  invertebrates  among 
animals.     The  most  important  modifications  that  discrimi- 


Fio.  509.  — 
Part  of  the  fruit- 
iug  stem  of  a 
scouring  rush, 
Equisctuin  limo- 
sum,  showing  the 
cone-like  spore 
cluster.  (After 
Gray.) 


354         PRACTICAL  COURSE  IN  BOTANY 

nate  the  two  groups  are :  (1)  the  presence  in  Pteridophytes 
of  a  highly  organized  vascular  system  accompanied  by  a 
well-marked  differentiation  of  the  plant  body  into  root  and 
stem ;  (2)  increased  importance  and  complexity  of  the  sporo- 
phyte  with  proportionate  diminution  of  the  gametophyte. 

While  vessels  for  conducting  water  occur  in  some  of  the 
bryophytes  (403),  a  well-defined  vascular  system  and  true 
roots  are  met  with  first  in  the  Pteridophytes.  The  change 
in  the  relative  importance  of  sporophyte  and  gametophyte 
is  so  marked  that  in  Selaginella,  the  genus  which  approaches 
nearest  in  structure  to  the  seed-bearing  plants,  the  suppres- 
sion of  the  gametophyte  has  proceeded  so  far  that  it  never 
leads  an  independent  existence  at  all  and  is  difficult  even  to 
recognize  as  a  distinct  individual. 

Practical  Questions 

1.'  Have  ferns  any  economic  use  —  that  is,  are  they  good  for  food, 
medicines,  etc.  ? 

2.  What  is  their  chief  value  ? 

3.  Under  what  ecological  conditions  do  they  grow  ? 

4.  Are  they  often  attacked  by  insects,  or  by  blights  and  disease  of 
any  kind  ? 

5.  Of  what  advantage  is  it  to  ferns  to  have  tlieir  stems  underground, 
in  the  form  of  rootstocks?     (321.) 

6.  What  causes  the  young  frond  of  ferns  to  unroll  ?     (54,  98.) 

7.  Name  the  ferns  indigenous  to  your  neighl^orhood. 

8.  Which  of  these  are  most  ornamental,  and  to  what  peculiarities  of 
structure  do  they  owe  that  quahty? 

9.  Are  cultivated  ferns  usually  raised  from  tha  spores  or  in  some 
other  way?     Why? 

10.  After  the  great  eruption  of  Krakatao  in  1883,  by  which  the  vege- 
tation of  the  island  was  completely  destroyed,  ferns  were  the  first  plants 
to  reappear.     Explain  why.     (19  ;  Exp.  17.) 

VIII.     THE    RELATION    BETWEEN    CRYPTOGAMS    AND 
SEED    PLANTS 

413.  No  break  in  the  chain  of  life.  —  The  great  gap  that 
was  once  supposed  to  exist  between  the  cryptogams  and 
phanerogams  has  been  bridged   over  by  the  discovery  of 


J 


CRYPTOGAMS  355 

analogies  in  the  reproductive  processes  of  the  two  groups 
that  connect  them  together  as  successive  links  in  one  continu- 
ous chain  of  vegetable  life.  It  is  therefore  very  important 
to  have  a  clear  understanding  of  the  nature  and  meaning  of 
these  processes,  for  the  chief  turning  points  in  the  life  his- 
tory of  the  different  groups  of  plants  are  connected  with 
them,  their  natural  relationships  to  each  other,  and  their 
distribution  according  to  their  respective  places  in  the  evolu- 
tionary scale,  being  determined  largely  by  a  comparison  of 
their  modes  of  continuing  the  life  of  the  group. 

414.  Alternation  of  generations  in  seed  plants.  —  This 
process,  so  conspicuous  among  Bryophytes  and  Pterido- 
phytes,  and  not  unknown  among  ThaDophytes,  is  universal 
among  seed  plants  (Spermatophytes)  also,  though  in  so 
masked  a  form  that  it  is  not  easy  to  recognize  without  a 
more  detailed  study  than  would  be  practicable  within  the 
limits  of  a  book  like  this.  Briefly,  we  may  say  that  the 
stamens  of  spermatophytes,  and  the  pistils,  or  rather  the 
carpels,  which  we  have  seen  to  be  transformed  leaves  (298), 
represent  the  sporophylls  (406)  of  the  higher  pteridophytes. 
The  pollen  sacs  and  ovules  are  sporangia,  bearing  micro- 
spores and  megaspores  (409),  represented  respectively  by 
the  pollen  grains  in  the  anther  and  the  embryo  sac  in  the 
ovule.  These  go  through  a  series  of  microscopic  changes  in 
the  body  of  the  ovule  analogous  to  the  production  of  the 
oospore  in  the  archegonia  of  ferns  and  liverworts,  but  the 
process  is  so  obscure  that  to  an  ordinary  observer  the  pollen 
grains  and  the  ovule  ippear  to  be  the  real  gametes,  and  were 
long  supposed  to  be  such.  The  fertilized  germ  cell  in  the 
embryo  sac  (251)  corresponds  to  an  oospore ;  the  embryo  sac 
with  the  endosperm  found  in  all  seeds  (previous  to  its  absorp- 
tion by  the  cotyledons)  is  a  rudimentary  gametophyte;  and 
the  embryo  in  the  matured  seed  is  the  undeveloped  sporo- 
phyte,  destined,  after  germination  and  further  growth,  to 
produce  a  new  generation  with  its  recurrent  cycle  of  alternat- 
ing phases. 


356 


PRACTICAL  COURSE  IN  BOTANY 


In  the  gymnosperms,  —  pines,  yews,  cycads,  etc., — which 
represent  the  most  ancient  and  primitive  type  of  existing 

seed-bearing  plants, 
the  similarity  of  these 
processes  to  those  of 
certain  of  the  pterido- 
phytes  is  very  striking, 
and  it  was  through 
the  study  of  these  that 
the  sequences  of  the 
process  were  traced  in 
the  much  more  obscure 
form  in  which  they 
occur  among  the  angi- 
osperms.  From  the 
endosperm  in  the  seeds 
of  gymnosperms  arche- 
gonia  were  found  to  be 
developed  (Fig.  510)  in 
much  the  same  way  as 

Fig.  510. -Diagrammatic  section  through  the  J^  Sclaginella,  from  the 
ovule  of  a  gymnospenn   belonging  to  the  spruce  "       ,      ' 

iamily:  z,  integument  covering  the  ovule  ;  e,  endo-  prothallium,     thuS 

sperm    (corresponding    to  female    gametophyte),  (jVinwino-   fViP    Ptirln 

which  fiUs  the  embryo  sac,  containing  two  arche-  SnOWlUg   tne    enOO- 

gonia,  a ;   o,  egg  cell ;   p,  pollen  grains ;   t,  pollen  sperm  tO  be  a  modified 
tubes  entering  the  neck,  c,  of  the  archegonia.  i  , ,  ,  , 

and  greatly  reduced 
gametophyte.  In  some  cases,  it  has  even  been  found  to 
protrude  a  little  way  out  of  the  embryo  sac  and  to  take  on 
a  slightly  greenish  tinge  —  another  remmiscence  of  its  origin. 
Fertilization,  too,  takes  place  in  ]:)recisely  the  same  manner 
as  in  the  pteridophytes,  except  that  in  all  but  the  ginkgo 
and  the  cycads,  the  fertilizing  cells  in  the  pollen  grains  are 
non-moi  ilo,  and  find  their  way  to  the  ovule  by  growing  down 
into  the  embryo  sac  with  the  pollen  tube,  instead  of  swimming 
to  it  —  an  adaptation  probably  brought  about  in  response 
to  changed  conditions  during  the  course  of  evolution  from 
aquatic  to  terrestrial  life. 


CRYPTOGAMS  357 

The  analogies  between  the  sequence  of  alternations  in  the 
two  classes  will  be  made  clearer  by  a  comparison  of  the 
accompanying  diagrams.  The  corresponding  terms  applietl 
to  the  various  organs  stand  in  the  same  vertical  row.  Dia- 
gram (1)  shows  the  process  as  it  takes  place  in  the  more 
highly  developed  Pteridophytes ;  diagram  (2)  the  corre- 
sponding phases  in  angiosperms. 

PTERIDOPHYTES 

<m.ospl >mic >mo >  anG *  ant >mg vv 
ybos >S 
Mospl >Mgc >Mo >arG y  arc >  fg f^ 

mospl,  micTOsporophyll ;  mic,  microsporangium  ;  mo,  microspores  ;  anG,  male 
gamctophyte  ;  ant,  antheridia  ;  7ng,  antherozoids.  The  letters  in  the  lower  line 
stand  for  the  corresponding  female  organs. 

SPERMATOPHYTES 


■2Ml ^/c  — ->  »io'— - 

de  veloped 

,     de  veloped 
.em ^end 37,;^,— 

gymno 
sperms 


st,  stamen  ;  an,  anther  ;  pol,  pollen  ;  fc,  food  cells  in  pollen  grain  ;  gc,  generative 
cell ;  p,  pistil ;  ov,  ovules  ;  cm,  embryo  sac  ;  end,  endosperm  ;  ec,  egg  cell. 

415.  Disappearance  of  the  gametophyte.  —  The  seed  is  a 
comparatively  recent  development  in  plant  evolution.  It 
has  no  counterpart  anywhere  among  the  cryptogams,  but  is 
strictly  characteristic  of  the  three  great  orders  of  Spermo- 
phytes:  Monocotyl,  Dicotyl,  and  Gymnosperms,  which 
compose  the  greater  part  of  the  vegetation  of  the  globe. 
Structurally,  it  is  a  matured  sporangium  containing  a  rudi- 
mentary sporophyte  (the  embryo),  and  a  reduced  gameto- 
phyte (the  embrj^o  sac),  which,  under  the  form  of  endosperm, 
has  dwindled  to  an  insignificance  that  makes  it  difficult  to 
recognize  it  as  a  phase  in  an  alternation  of  generations. 

416.  Significance  of  the  sporophyte.  —  The  gametophyte 
is  obviously  a  more  ancient  and  primitive  structure  than  the 
sporophyte,  which  first  becomes  prominent  in  the  ferns  and 


358  PRACTICAL  COURSE  IN  BOTANY 

their  allies.  The  sudden  and  violent  break  in  the  succession 
of  vegetable  life  that  accompanies  the  appearance  of  the 
pteridophytes  (412)  is  probably  to  be  explained  by  the 
development  of  a  land  flora  and  the  necessity  of  adaptation  to 
life  in  a  new  medium.  The  fact  that  no  living  cell,  whether 
vegetable  or  animal,  can  absorb  nourishment  except  in  a 
liquid  form,  seems  to  point  to  an  aquatic  origin  more  or  less 
remote  for  all  life.  This  inference  is  further  strengthened, 
in  the  case  of  plants,  by  the  fact  that  even  in  so  highly  or- 
ganized a  group  as  the  pteridophytes,  fertilization  cannot 
take  place  except  in  water.  Such  a  requirement  would 
manifestly  be  a  great  disadvantage  to  land  plants,  and  one 
of  the  first  steps  in  response  to  the  demands  of  a  new  habitat 
would  be  to  get  rid,  as  far  as  possible,  of  the  primitive  game- 
tophyte  with  its  outgrown  adaptations  to  a  liquid  medium, 
and  to  transfer  the  greater  part  of  the  work  of  reproduction 
to  the  asexual  generation,  in  which  the  problem  of  fertiliza- 
tion did  not  have  to  be  directly  met,  the  asexual  spores  ger- 
minating without  it.  The  greater  the  number  of  these 
produced,  the  better  the  chance  that  at  least  some  of  the 
gametes  developed  from  them  would  meet  the  difficult  con- 
ditions of  fertilization,  and  the  survival  of  the  species  be 
assured.  At  the  same  time,  in  order  to  meet  the  requirements 
of  terrestrial  life  successfully,  and  to  provide  for  continuing 
the  sexual  generation,  correlative  changes  would  have  to 
take  place  in  the  gametophyte  by  which  the  increasing 
uncertainty  of  fertilization  due  to  structural  changes  in  the 
sporophyte,  and  the  absence  of  a  liquid  medium  for  the  con- 
veyance of  free  swimming  antherozoids  would  be  avoided. 
This  necessity  has  been  met  by  the  development  of  the  pollen 
tube,  which  bores  its  way  to  the  egg  cell,  carrying  with  it  the 
generative  cells,  which  in  seed  plants  have  taken  the  place 
of  the  more  primitive  antherozoids.  With  the  concomitant 
reduction  of  the  gametophyte  and  development  of  the  seed 
habit,  the  adaptation  to  land  conditions  has  been  made 
complete. 


CRYPTOGAMS  359 

Roughly  speaking,  it  may  be  said :  (1)  that  Thallophytes 
are  predominantly  aquatic ;  (2)  Archegoniates  (Bryophytes 
and  Pteridophytes),  amphibious;  (3)  Spermophytes,  terres- 
trial; (4)  that  the  seed  habit  is  a  response  to  terrestrial 
conditions;  and  (5)  that  the  increased  development  of  the 
sporophyte  was  a  necessary  adaptation  to  meet  those  condi- 
tions. 


IX.    THE   COURSE   OF  PLANT  EVOLUTION 

417.  Plant  genealogy.  —  It  has  been  shown  by  a  study  of 
existing  forms  of  plant  life  that  there  is  no  hard  and  fast 
line  of  division  anywhere  between  the  different  groups,  but 
that  they  are  all  connected  by  ties  of  kinship  more  or  less 
defined,  according  to  their  distance  from  a  common  ancestral 
stock.  The  geological  record  points  to  the  same  conclusion, 
and  our  classification  of  them  into  families,  orders,  and  spe- 
cies is  merely  a  very  imperfect  genealogical  table  of  their 
supposed  pedigrees.  This  does  not  mean,  however,  that  we 
can  assert  positively  that  such  and  such  a  species  is  derived 
from  such  or  such  another,  but  that  both  are  descended  from 
some  common  intermediate  form  more  or  less  remote.  While 
we  have  reason  to  believe  that  the  flowering  plants  are  de- 
rived through  pteridophyte  and  bryophyte  types  from  some 
of  the  green  algae,  no  direct  connection  has  ever  been  traced 
between  any  particular  kind  of  flowering  plant  and  any  par- 
ticular kind  of  alga,  —  or  between  a  liverwort  and  an  alga, 
for  that  matter,  —  and  probably  never  will  be,  because  the  in- 
termediate forms  die  out,  or  pass  on  by  variation  into  other 
lines  of  development.  But  while  this  is  true,  all  the  evidence 
we  possess  does  go  to  show  that,  since  the  beginning  of  life 
on  the  globe,  there  has  been  a  general  progressive  evolution 
from  lower  and  simpler  to  higher  and  more  complex  forms. 

418.  Retrogressive  evolution.  —  AVhile  the  general  course 
of  evolution  has  been  upward  and  onward,  the  movement  has 
not  always  followed  a  straight  line,  but,  like  a  mountain  road, 


3G0  PRACTICAL  COURSE  IN  BOTANY 

shows  many  windings  and  deviations  from  the  direct  route. 
The  monocotyls  furnish  a  conspicuous  example  of  this  de- 
parture from  the  general  law  of  progression.  It  was  formerly 
supposed,  on  account  of  their  greater  simplicity  of  structure, 
that  they  were  a  more  ancient  type  than  dicotyls,  but  recent 
investigations  point  to  the  conclusion  that  they  are  a  later 
offshoot,  derived  from  some  primitive  form  of  aquatic  dicotyl, 
and  represent,  not  an  ancient  aT5d  primitive  stock,  but  a  case 
of  retrogressive  evolution  from  a  higher  type.  Strong  pre- 
sumptions in  favor  of  this  view  are  :  (1)  that  various  species 
of  dicotyls  show  an  unequal  development  of  the  seed  leaves, 
amounting,  in  the  bryony,  to  complete  abortion  of  one  of 
them,  while  some  monocotyl  seeds  show  morphological 
characters  that  can  best  be  explained  as  survivals,  or  inherit- 
ances, from  a  dicotyl  ancestor;  (2)  the  structural  resem- 
blances between  gymnosperms  and  dicotyls  are  closer  than 
between  gymnosperms  and  monocotyls,  which  could  hardly 
be  the  case  if  the  latter  were  the  more  ancient ;  (3)  the  geo- 
logical record  does  not  show  them  to  have  appeared  before 
dicotyls  ;  (4)  the  number  of  cotyledons  furnishes  no  criterion 
as  to  the  relative  age  of  any  plant  group,  since  all  three  types 
are  represented  among  the  pteridophytes,  where  plants  are 
found  bearing  one,  two,  or  more  cotyledons. 

The  theory  of  their  comparatively  recent  origin  from  an 
aquatic  ancestor  is  further  borne  out  by  the  many  points  of 
similarity  between  their  internal  structure  and  that  of  hy- 
drophytes (318),  and  also  by  the  great  proportion  of  aquatio 
plants  among  them,  amounting  to  thirty- three  per  cent,  while 
in  dicotyls  the  proportion  is  only  four  per  cent.  Can  you 
give  any  reasons,  from  your  examination  of  their  internal 
structure  (113,  114),  for  believing  that  the  line  of  develop- 
ment which  they  have  followed  is  a  less  effective  one  for 
meeting  conditions  now  existing  on  the  globe  than  that  at- 
tained by  dicotyls  ? 

We  should  remember,  too,  that  while  progressive  evolution 
implies  successful  adjustment  to  surroundings,  it  is  possible 


CRYPTOGAMS 


361 


to  conceive  of  a  state,  as  our  planet  approaches  the  period 
of  cosmic  debility  and  decay,  when  the  conditions  of  existence 
may  become  progressively  more  and  more  unfavorable.  In 
this  case  the  course  of  evolution  would  be  reversed,  the  higher 
types  gradually  dying  out  as  the  struggle  for  life  became 
more  severe,  and  the  tendency  would  be  constantly  toward 
lower  and  simpler  forms,  until  finally  all  life  would  become 
extinct  on  our  planet. 
We  have  no  right,  how- 
ever, to  assume  that 
during  such  a  course  of 
retrogressive  evolution 
the  same  forms  would 
be  repeated  in  reverse 
order  as  have  already 
appeared,  because 
there  is  no  reason  to 
believe  that  the  condi- 
tions brought  about  by 
planetary  decline  and 
"old  age"  would  be 
the  same  as  those  at- 
tending planetary 
birth  and  adolescence. 
419.  Explanation  of 
the  diagram.  —  An  at- 
tempt  to  show  the 
general  course  of  plant 
evolution  up  to  the  present  time  is  made  in  the  accompany- 
ing diagram.  The  four  great  divisions,  Thallophytes,  Brj'o- 
phytes,  Pteridophytes,  and  Spermatophytes,  are  represented 
by  spaces  between  four  horizontal  lines  arranged  one  above 
the  other  in  the  order  of  their  succession  in  time  and  com- 
plexity of  organization.  It  should  be  borne  in  mind  that 
these  dividing  lines  are  not  sharply  defined  in  nature,  but 
overlap  or  indent  the  territory  between  them  with  vary- 


Thallophytes 


Fig. 


511.  —  Diagram   showing  the  supposed 
course  of  plant  evolution. 


362         PRACTICAL  COURSE  IN  BOTANY 

ing  degrees  of  irregularity,  like  the  coast  line  on  a  map. 
The  relative  positions  of  the  different  orders  we  have 
been  considering  are  represented  by  upright  and  diagonal 
lines,  the  general  course  of  which,  as  indicated  by  the 
arrows,  is  intended  to  give  an  idea  of  the  trend  of  evolu- 
tionary progress  in  the  particular  group  represented  by  each 
line.  No  one  of  these  lines  is  made  to  originate  directly  in 
any  other,  because,  with  the  possible  exception  of  the  mono- 
cotyls,  we  have  no  authority  for  asserting  that  any  such  direct 
connection  exists  between  plants  as  we  know  them,  but  only 
that  certain  types  give  evidence  of  descent  from  a  common 
ancestry.  This  lack  of  certainty  is  expressed  by  placing  the 
point  of  origin  for  any  given  line  in  more  or  less  close  proxim- 
ity to  the  one  which  is  supposed  to  be  the  nearest  living 
representative  of  the  common  ancestor.  The  line  of  ferns, 
for  instance,  is  depicted  as  originating  in  the  region  of  the 
bryophytes,  somewhere  in  the  neighborhood  of  the  liverworts, 
but  the  two  lines  nowhere  come  in  contact,  because  there  is 
no  evidence  that  any  fern,  living  or  fossil,  is  directly  de- 
scended from  any  particular  kind  of  liverwort  known  to  us. 
With  these  explanations,  the  diagram  shows,  in  a  rough  way, 
the  generally  accepted  view  of  plant  relationships  as  based  on 
the  evidence  at  present  before  us.  But  in  questions  of  this 
sort  it  is  wise  to  keep  in  mind  the  blunt  remark  of  a  famous 
old  American  statesman,  that  ''only  fools  and  dead  people 
never  change  their  opinions." 

Field  Work 

1.  If  you  live  in  the  country,  study  the  appearance  of  plants  affected 
with  bhghts,  smuts,  rusts,  and  mildews,  and  learn  to  recognize  the  different 
kinds  of  disease  by  their  signs.  Notice  which  kinds  are  most  prevalent  in 
your  neighborhood,  and  what  plants  are  most  affected  by  them. 

2.  Notice  the  different  kinds  of  mushrooms  you  find  growing  wild. 
Observe  the  difference  between  those  that  grow  on  the  ground  and  those 
that  grow  on  logs,  stumps,  and  trees ;  between  those  found  in  the  woods 
and  those  in  open  ground.  Find  out  how  those  on  the  ground  get  their 
nourishment.     Uncover  the  mycelium,  and  notice  the  extent  of  its  surface. 


CRYPTOGAMS  353 

Examine  the  soil  and  find  out  if  it  contains  anything  upon  which  they 
could  feed.  Note  the  prevalence  of  shelf  fungi  on  trees.  Examine  the 
condition  of  the  wood  where  they  grow,  and  decide  in  what  ways  they 
injure  their  hosts.  Notice  whether  they  abound  most  on  healthy  or  on 
decaying  trunks  and  boughs,  and  decide  whether  this  is  because  the 
fungus  i)refers  that  kind  of  host,  or  whether  the  injury  it  does  causes 
the  decay,  or  whether  both  causes  operate  together.  Notice  what  fungi 
grow  on  different  trees,  and  study  their  preferences  in  this  respect. 

3.  Observe  the  different  kinds  of  lichens  found  in  your  walks  and  try 
to  distinguish  the  three  classes.  Which  kind  are  most  abundant  in  your 
neighborhood  ?  Which  least  so  ?  Note  the  situations  in  which  you  find 
each  kind  growing,  whether  on  stumps,  trees,  rocks,  or  the  ground.  Con- 
sider how  the  algae  and  fungi  aid  each  other  in  the  different  positions: 
could  either,  for  instance,  exist  independently  on  bald  rocks  ?  Notice  on 
what  kind  of  trees  the  different  lichens  seem  to  thrive  best  and  on  which 
poorly  or  not  at  all,  and  whether  the  character  of  the  bark  —  rough, 
smooth,  scaly — has  anything  to  do  with  their  choice  of  a  habitat. 


APPENDIX 
SYSTEMATIC   BOTANY 

Taxonomy,  or  systematic  botany,  deals  with  the  family 
relationships  of  plants  in  the  order  of  their  nearness  or  re- 
moteness with  regard  to  a  common  line  of  descent.  Its  chief 
value  is  the  insight  it  gives  into  the  course  of  plant  evolution 
and  into  the  nature  of  the  modifications  that  differentiate 
each  group  from  the  ancestral  type.  While  it  is  not  ad- 
visable to  spend  too  much  time  in  the  mere  identification  of 
species,  a  sufficient  number  should  be  examined  and  de- 
scribed to  familiarize  the  student  with  the  distinctive 
characteristics  of  the  principal  botanical  orders. 

Principles  of  classification.  —  All  the  known  plants  in  the 
world,  numbering  not  less  than  one  hundred  and  twenty 
thousand  species  of  the  seed-bearing  kind  alone,  are  ranged 
according  to  certain  resemblances  of  structure,  into  a  number 
of  great  groups  known  as  families  or  orders.  The  names 
of  these  families  are  distinguished  by  the  ending  acece;  the 
rose  family,  for  instance,  are  the  Rosacece;  the  pink  family, 
Canjophyllacece;  the  walnut  family,  Juglandacece,  etc.  Each 
of  these  families  is  divided  into  lesser  groups  called  genera 
(singular,  genus),  characterized  by  similarities  showing  a 
still  greater  degree  of  affinity  than  that  which  marks  the 
larger  groups  or  orders;  and  finally,  when  the  differences 
between  the  individual  plants  of  a  kind  are  so  small  as  to  be 
disregarded,  they  are  considered  to  form  one  species;  all  the 
common  morning-glories,  for  instance,  of  whatever  shade  or 
color,  belong  to  the  species  Ipomea  purpurea.  The  small 
differences  that  arise  within  a  species  as  to  the  color  and 
364 


APPENDIX  365 

size  of  flowers,  and  other  minor  points,  constitute  mere 
varieties,  and  have  no  special  names  appUed  to  them.  The 
Une  between  varieties  and  species  is  not  clearly  defined,  and 
in  the  nature  of  things  can  never  be,  since  progressive  de- 
velopment, through  unceasing  change,  is  the  law  of  all 
life. 

In  botanical  descriptions,  the  name  both  of  the  species 
and  the  genus  is  given,  just  as  in  designating  a  person,  like 
Mary  Jones  or  John  Robinson,  we  give  both  the  surname 
and  the  Christian  name.  The  genus,  or  generic  name, 
answers  to  the  surname,  and  that  of  the  species  to  the 
Christian  name  —  except  that  in  botanical  nomenclature 
the  order  is  reversed,  the  generic,  or  surname,  coming  first, 
and  the  specific  or  individual  name  last;  for  example, 
Ipomea  is  the  generic,  or  surname,  of  the  morning-glories,  and 
purpurea  the  specific  one. 

How  to  use  the  key.  —  Any  good  manual  will  answer  the 
purpose.  Gray's  "  School  and  Field  Book  "  is,  perhaps,  the 
best  available  at  present  for  the  states  east  of  the  Missis- 
sippi. Reference  to  the  floral  analyses  in  sections  I-IV  of 
Chapter  VII  will  make  its  use  clear.  Suppose,  for  instance, 
we  want  to  find  out  to  what  botanical  species  the  morning- 
glory  or  the  sweet  potato  belongs.  Turning  to  the  key, 
we  find  the  sub-kingdom  of  Phaenerogams  —  flowering  or 
seed-bearing  plants  —  divided  into  two  great  classes,  Angio- 
sperms  and  Gymnosperms,  as  explained  in  18.  A  glance  will 
show  that  our  specimen  belongs  to  the  former  class.  Angio- 
sperms,  again,  are  divided  into  the  two  subclasses  of  Dicotyle- 
dons and  Monocotyledons  (18,  171).  We  at  once  recognize 
our  plant,  by  its  net-veined  leaves  and  pentamerous  flowers, 
as  a  dicotyledon  (171,  229),  and  turning  again  to  the  key, 
we  find  this  subclass  divided  into  three  great  groups :  Sym- 
petalous (211),  called  also  Monopetalous  and  Gamopetalous  ; 
Apopetalous,  or  Polypetalous  (211),  and  Apetalous — having 
no  petals  or  corolla.  A  glance  will  refer  our  blossom  to  the 
sympetalous  or  monopetalous  group,  which  we  find  divided 


366  APPENDIX 

into  two  sections,  characterized  by  the  superior  or  inferior 
ovary  (218,  225).  Further  examination  will  show  that  the 
morning-glory  belongs  to  the  former  class,  which  is  in  turn 
divided  into  two  sections,  according  as  the  corolla  is  regular, 
or  more  or  less  irregular.  We  see  at  once  that  we  must  look 
for  our  specimen  in  the  group  having  regular  corollas.  This 
we  find  again  subdivided  into  four  sections,  according  to  the 
number  and  position  of  the  stamens,  and  we  find  that  the 
morning-glory  falls  under  the  last  of  these,  —  "  Stamens  as 
many  as  the  lobes  or  parts  of  the  corolla  and  alternate 
with  them."  A  very  little  further  search  brings  us  to  the 
family  Convolvulacece,  and  turning  to  that  title  in  the  de- 
scriptive analysis,  we  find  under  the  genus,  Ipomea,  a  full 
description  of  the  common  morning-glory,  in  the  species 
Ipomea  purpurea,  and  of  the  sweet  potato  in  the  species 
Ipomea  batatas. 

Making  collections.  — Mere  labeled  aggregations  of  species 
are  not  recommended,  but  the  collection  of  examples  illus- 
trating special  points  in  morphology  and  plant  variation 
may  be  made  with  profit;  such,  for  instance,  as  the  adapta- 
tions Observed  in  tendrils  and  stipular  appendages,  the 
various  modifications  of  leaves  and  stems  to  serve  other 
than  their  normal  purposes,  or  the  different  forms  of  leaves 
and  flowers  on  the  same  stem,  or  on  different  plants  of  the 
same  species.  A  collection  made  with  some  specific  object 
in  view  would  also  be  instructive,  and  might  prove  of  great 
value ;  for  instance,  to  get  together  examples  of  all  the 
troublesome  weeds  of  a  locality  for  the  purpose  of  studying 
their  habits  and  devising  means  for  their  eradication ;  or  of 
all  the  native  useful  plants,  with  detailed  analyses  of  their 
economic  properties,  and  observations  on  their  habits  and  the 
practicability  of  further  developing  them.  In  short,  wherever 
collecting  is  carried  on,  it  should  be  done  with  some  object 
other  than  the  mere  identification  of  species,  which  often 
results  in  greater  detriment  to  the  wild  plants  of  a  neighbor- 
hood than  profit  to  the  collector. 


APPENDIX 


367 


WEIGHTS,   MEASURES,   AND   TEMPERATURES 

As  the  metric  system  of  weights  and  measures  and  the 
Centigrade  appraisement  of  temperatures  are  universally- 
employed  in  scientific  works,  the  following  tables  showing 
the  equivalents  in  our  common  English  standards  of  those 
in  most  frequent  use,  are  given  for  the  convenience  of 
students  who  have  not  already  familiarized  themselves  with 
the  subject.  The  values  given  are  approximate  only,  but  will 
answer  for  all  practical  purposes,  except  in  cases  where  very 
great  exactitude  is  required.  The  micron,  or  micrometer, 
is  used  principally  by  scientific  investigators  for  measuring 
extremely  minute  objects  seen  under  the  microscope. 

Measures  op  Length 


Metric 

English  Equivalents 

Kilometer   . 

. 

km. 

1  of  a  mile. 

Meter     .     . 

m. 

39  inches. 

Decimeter  . 

• 

dm. 

4  inches. 

Centimeter 

cm. 

1  of  an  inch. 

Millimeter  . 

mm. 

5^  of  an  inch. 

Micron.  .     . 

/* 

^zh^  of  an  inch. 

Capacity 


Liter  

1. 

61  cubic  inches,  or  1  quart,  U.S.  measure 

Cubic  centimeter 

cc. 

xV  of  a  cubic  inch. 

Weight 


Kilogram    .     .     .    kg.,  or  kilo 


Gram 


gm. 


2i  pounds. 


15^-  grains  avoirdupois. 
^j  of  an  oxmce  avoirdupois. 


368 


APPENDIX 

Metric  and  English  Scai 


10  CENTIMETER5  =  I  DECIMETER 

11  2  3  41  51  61  7 


l06:;Kl'lLUMeTER5| 


iiiiiiiiniiiiiiiiiiiii 


IT  I 


rnr 


TTJ 


TTT 


m 


I  2 

4  INCHES 


TTT 


Temperature   Equivalents 

The  next  table  gives  the  Fahrenheit  equivalent,  in  round 
numbers,  for  every  tenth  degree  Centigrade  from  absolute 
zero  to  the  boiling  point  of  water.  To  find  the  correspond- 
ing F.  for  any  degree  C,  multiply  the  given  C.  temperature 
by  nine,  divide  by  five,  and  add  thirty- two.  Conversely, 
to  change  F.  to  C.  equivalent,  subtract  thirty-two,  multiply 
by  five,  and  divide  by  nine. 


Cent. 


Fahr. 


Cent. 


Fahr. 


100  ..  . 

...  212 

0 

.   32 

90  .  .  . 

...  194 

-  10 

.   14 

80  .  .  . 

...  176 

-  20 

-  4 

70  .  .  . 

.  .  .  1.58 

-  30 

-  22 

60  .  .  . 

...  140 

-  40 

-  40 

50  .  .  . 

...  122 

-  50 

-  58 

40  .  .  . 

...  104 

-100 

-148 

30  .  .  . 

...   86 
...   68 

20  .  .  . 

Absolute  zero. 

10  .  .  . 

...   50 

-273 

-459 

INDEX 


(The  numbers,  unloss  otherwises  desigtiated,  refer  to  paragraphs.) 


Aborted,  220,  291. 

Absorption,  58,  71,  72  ;  Exp.  39. 
selective,  60. 

Accessory  buds,  158. 

Accessory  fruits,  302. 

Adaptation,  206,  237. 

Adhesive  fruits,  20;  Exp.  20. 

Adjustment  of  leaves,  196-202. 

Adnate,  374. 

Adventitious  buds,  65,  158. 

Adventitious  roots,  37,  83. 

^cidium,  362. 

Aeration,  319. 

Aerial  roots,  88. 

Aggregate  fruits,  301,  303, 

Air  space,  114,  116,  184. 

Akene,  234,  296,  302,  305. 

Albumin,  3. 

Albuminous,  56. 

Albuminous  seed,  i.e.,  containing   endo- 
sperm; Field  work,  p.  28, 

Aleurone,  3. 

Algffi,  333,  336-342. 

Alternate  leaves,  168. 

Alternation  of  generations,  395,  400,  409, 
414. 

Analogous,  108. 

Anatropous,  Fig.  20. 

Angiosperms,  15,  18  ;  Fig.  51 1. 

Annuals,  91. 

Annulus,  372,  405. 

Anther,  213,  235;  Figs.  270-274. 

Antheridia,  389,  394,  398,  407, 

Antheridial,  388. 

Antherozoids,  389,  392,  395,  416. 

Antisepsis,  355. 

Arch  of  the  hypocotyl,  42,  44. 

Archegonia,  390,  394,  407,  408. 

Archegonial,  388. 

Archegoniates,  408,  416. 

Archegonium,  391,  394,  398. 

Asexual  generation,  395.  399,  409,  416. 

Asexual  reproduction,  394,  395. 

Asexual  apore,  395,  407,  409,  410,  416. 

Assurgent,  95. 

Axial  placenta,  216,  300, 

Axil,  100,  166. 

Axillary  buds,  145. 

Axis,  64,  65,  79,  152,  156,  159,  161, 


Bacillus,  348,  349. 

Bacteria,  333,  345,  347-353. 

Bark,  118,  119,  122,  p.  128,  (3). 

Basidia,  375. 

Bast,  116,  119,  122. 

Berry,  291. 

Biennial,  92. 

BUabiate,  237,  243. 

Bilateral  regularity,  219. 

Bilateral  zonation,  326. 

Black  rust,  360. 

Blade  of  leaf,  165. 

Biogenetic  law,  253. 

Biological  factors,  309. 

Bordered  pits,  114,  117  ;  Fig.  123. 

Boreal,  329. 

Bract,  161. 

Bryophytes,  334,  385-401. 

Bud  scales,  147-149. 

Buds,  145,  155-158. 

Bulb,  107. 

Button  (of  mushroom),  370. 

Calyptra,  399. 

Calyx,  211. 

Cambium,  115,  110,  120,  123. 

Cap,  372,  373. 

Capillarity,  136;  Exp.  53. 

Capitate,  220. 

Caprification,  279.  305. 

Caprifig,  279. 

Capsule,  298. 

Carbon,  27,  28,  62. 

Carbon  dioxide,  29,  63,  185, 186, 187,  189, 

Exps.  23,  25. 
Carpels,  216,  288. 
Caruncle,  13. 
Catkin,  161. 
Caulicle,  46. 
Cedar  apples.  Fig.  456. 
Cell,  6,  7. 

collecting,  184. 

companion,  114. 
Cell  sap,  7.  110. 
Cell  wall.  7,  183. 
Central  cylinder,  67. 
Central  placenta,  216,  .300. 
Chalaza,  13. 
Chlorophyll,  186,  341,  366. 


369 


370 


INDEX 


ChlorophyU  bodies,  184.  186,  382. 

Cion,  65, 

Classification,  90,  252,  283,  343,  384,  411 

417. 
Cleistogamic  flowers,  272. 
Climatic  zones,  329. 
Climbing  stems,  96-98. 
Clipped  seed,  p.  12  (material). 
Closed  bundle,  114. 
Close-fertilized,  272. 
Cluster  cups,  362. 
Coccus  (pi.  cocci),  339,  348. 
Coiled  inflorescence,  162. 
Collective  fruits,  304. 
Colony,  316,  337,  357. 
Color  of  flowers,  276. 
Compass  plants,  199. 
Complete  flower,  219. 
Composite,  235,  381. 
Composite  flower,  236. 
Compound  leaf,  178. 
Conduplicate,  Figs.  159,  160. 
Confluent,  404. 
Conifers,  117,327. 
Conjugation,  342,  394. 
Corolla,  211. 
Cortex,  64,  115,  122. 
Corymb,  161. 
Cotyledon,  11,  12,  18. 
Cross  cut,  133. 
Cross  fertilization,  255. 
Cross  pollination,  255. 
Crustaceous  lichen,  384. 
Cryptogam,  332. 
Crystalloids,  60. 

Culture  medium,  347;  p.  306  (material). 
Cycle,  217,  219,  229. 
Cycle  of  growth,  50. 
Cyme,  162. 

Cymose  inflorescence,  162. 
Cypress  knees,  319. 

Deciduous,  203. 
Declined,  95. 
Decurrent,  374. 
Definite  annual  growth,  153. 
Definite  inflorescence,  160,  162. 
Dehiscent  fruits,  283,  298. 
Deliquescent,  144. 
Determinate  growth,  153. 
Determinate  inflorescence,  160,  162. 
Diadelphous,  239. 
Diastase,  9. 
Dichogamy,  269. 
Dichotomous,  152;   Fig.  155. 
Dicotyl,  42,  115,  116,  171;  220. 
Dicotyledonous,  12. 
Differentiate,  245,  345,  409. 
DifTusion,  9,  57. 


Digestion,  9. 
Dimorphic,  270. 
Dimorphism,  270. 
Dimorphous,  270. 
Dioecious,  268. 
Disinfection,  355. 
Disk  flower,  233. 
Dispersal  of  seed,  19-25. 
Dominant,  257,  258. 
Dormant  buds,  157. 
Dorsal ;  Figs.  390,  391. 
Drupe,  292. 

Dry  fruits,  283,  293-300. 
Duct,  67,  111,  114. 

Ecological  factors,  310. 

Ecology,  266,  308,  310. 

Edgings,  134. 

Egg  cefl,  251,  391. 

Elators,  393. 

Embryo,  11. 

Embryology,  253. 

Embryo  sac,  251. 

Endodermis,  67  (b). 

Endosperm,  11,  13,  14,  16,  17,  414. 

Epicotyl,  45,  46,  47. 

Epidermis,  64,  115,  122,  183. 

Epigynous,  225,  230. 

Epiphyte,  87,  394. 

Essential  constituents,  62. 

Essential  organs,  212. 

Evolution,  242,  245,  265,  334,   335,  401, 

414,  415,  417,  418,   419. 
Evolutionary,  253,  413. 
Excentric  attachment,  372. 
Excurrent,  144,  154. 

Factors,  54,  265,  310. 

Fall  of  the  leaf,  203. 

Fascicled  roots,  80,  81. 

Fats,  1,  3,  4. 

Feather-veined,  172. 

Ferments,  9,  356. 

Fertile,  404. 

Fertile  flower,  267. 

Fertilization,    247,    251,    252.    392,  408, 

416. 
Fibrous  roots,  37,  78,  80,  81. 
Fibrovascular  bundle,  67,   114,  116,  176, 

288. 
Fig  wasp,  279. 
Filament  of  the  stamen,  213;    a  hairlike 

appendage,  341,  361,  369,  393,  396. 
Filamentous  algae,  340,  341. 
Fission,  338,  394. 
Fleshy  fruits,  283,  288-292. 
Floral  envelopes,  211. 
Foliacoous  lichen,  379,  384. 
FoUicle,  298. 


INDEX 


371 


Forestry,  139-142. 

Forked  stems,  152. 

Formation,  316. 

Free,  218,  374. 

Free  central  placenta,  216. 

Free  gills,  374. 

Free  ovary,  218. 

Free  veining,  402. 

Freezing,  33. 

Frog's  spit,  340. 

Frond,  402. 

Fruit,  282. 

Fruticose  lichen,  384. 

Function,  41. 

Fungi,  333,  343,  344,  345,  346,  378. 

Fungus,  86,  364. 

Gametes,  394. 

Gametophyte,   394,   395,   396,  406,   407, 

410,  412,  414,  415,  416. 
Gemmae,  387. 
Generative  cell,  249,  416. 
Geophilous,  321. 
Geotropism,  51,  52,  53. 
Germ,  2,  11. 
Germ  cell,  251,  414. 

Germination,   32,  35;    E.xps.  25,  26-29. 
Germs,  352,  355. 
Gills  (of  mushroom),  374. 
Girdling,  131. 
Glutin,  3. 
Gourd,  14,  290. 
Grain,  11,  297. 

Grain  of  timber,  133,  134,  135. 
Gravity,  52. 
Growth,  48-52,  179. 
Guard  cell,  183. 

Gymnosperms,  15,  18,  117,  414. 
Gymnosporangium,  Fig.  456. 

Halophyte,  317,  323. 

Haustoria,  85. 

Hay  bacillus,  348,  349. 

Head,  161. 

Heartwood,  131. 

Hcliotropic,  200. 

Heliotropism,  198. 

Herbaceous,  90,  94,  115,  116. 

Heredity,  264,  265. 

Hilum,  12,  13,  14. 

Homologous,  108. 

Host  plant,  85. 

Humus,  75,  86. 

Hybrid,  256. 

Hybridization,  256,  257,  263. 

Hydrophytes,  317,  318,  319. 

Hymenium,  375. 

Hymenomycetes,  375. 

Hyphae  (slug,  hypha),  369,  380. 


Hypoootyl,  11,  12,  14,  46. 

arched,  42,  44. 

straight,  44. 
Hypogynous,  218,  225. 

Imbibition,  136. 

Imperfect  flower,  219,  231,  267. 

Impure  hybrid,  258,  259. 

In-breeding,  254. 

Incomplete  flower,  219. 

Incubation,  354. 

Indefinite  annual  growth,  153. 

Indefinite  inflorescence,  160,  161. 

Indefinite  number  of  parts,  229. 

Indehiscent  fruit,  283,  294. 

Indeterminate  growth,  153. 

Indeterminate  inflorescence,  160,  161. 

Indusium,  404. 

Inferior  ovary,  221,  225. 

Inflorescence,  159. 

Insectivorous  plants,  208-210. 

Internode,  46,  110;    Exp.  35. 

Invasion,  328. 

Inverted  seed,  14. 

Involucre,  161,  232. 

Involute,  373;   Fig.  251. 

Iodine  solution,  Exp.  3. 

Irregular  flower,  219,  237. 

Irritability,  201. 

Joint,  110,  113. 

Keel,  238. 
Knots,  137. 

Lamina,  209. 

Laminae,  368,  374. 

Lateral,  372,  398. 

Lateral  buds,  145. 

Leaf  attachment,  167. 

Leaf  cups,  202. 

Loaf  scars,  146. 

Leaf  traces,  146. 

Legume,  299. 

Lenticels.  106,  118,  288. 

Lichen,  379. 

Life  cycle,  359,  364. 

Loam,  75. 

Lobing,  177;  Figs.  210-212. 

Locule,  216. 

Loment,  Fig.  394. 

Lyrate,  Fig.  197. 

Medulla,  119,  122. 

Medullary  rays,  64,  116, 121, 122, 134, 135. 

Megasporangia,  409. 

Mcgaspore,  409,  414. 

Mendel's  law,  258. 

Mesophyte,  317,  324. 


372 


INDEX 


Metabolism,  193. 

Microbe,  351,355. 

Micrococcus,  339. 

Micropyle,  12,  13,  14.  15,  45. 

Microsporangia,  409. 

Microspore,  409,  414. 

Midrib,  172. 

Mixed  forest,  139,  324. 

Modification,  100-108,  206,  207,  289. 

Molecule,  136. 

Monadelphous,  239. 

Monocotyl,  110,  112,  171,  217,  221,418. 

Monocotyledonous.  11. 

MoncBcious,  268. 

Monopetalous,  211. 

Monosepalous,  211. 

Morphology,  108. 

of  the  flower,  244. 
Mosaic  (leaf),  197. 
Mosses,  334,  396-401. 
Muck,  75. 

Multiple  fruit,  304,  305. 
Mushroom,  333,  367. 
Mutation,  264. 
Mycelium,  343,  359,  369. 
Mychorrhiza,  86. 

Neck  canal,  391. 
Net-veined,  171. 
Neuter,  267. 

Neutral  flower,  231,  267. 
Nitrogen,  62,  63,  188. 
Nitrogenous  food,  188. 
Node,  46,  65,  110,  113. 
Nucleus,  7,  341. 
Numerical  plan,  217,  229. 
Nut,  295. 
Nutriment,  3,  186. 
Nutrition,  50,  54,  179,  193. 
Nyctitropic,  200. 

Obsolete,  220. 

Oil,  1,  3,  8. 

Oospore,  393,  394, 395. 

Open  bundle,  116. 

Operculum,  399. 

Opposite  leaves,  168. 

Organ,  41. 

Organic  foods,  4. 

Organs  of  reproduction,  40. 

of  vegetation,  40. 
Osmosis,  56,  57. 
Ovary,  214,  216,  223. 
Ovule,  216. 

Oxidation,  27 ;   Exps.  21,  22. 
Oxygen,  62,  63,  186,  187 ;   Exps.  22,  66. 

Palisade  cells,  184. 
Palmate  veining,  172. 


Panicle,  Fig.  171. 

Papilionaceous,  237,  238. 

Pappus,  234. 

Parallel  veining,  171. 

Paraphyses,  375,  398. 

Parasitic,  5,  345,  364. 

Parasitic  plants,  85,  343,  382. 

Parenchyma,  110,  114,  115. 

Parietal,  216. 

Pathogenic,  352,  353. 

Pedicel,  159. 

Peduncle,  159,  288. 

Pentamerous,  229. 

Pepo,  290. 

Perennial,  93. 

Perfect  flower,  219. 

Perianth,  211. 

Pericarp,  288. 

Perigynous,  Figs.  301,  302. 

Persistent,  166. 

Petals,  211. 

Petiole,  165. 

Phanerogams,  331,  332. 

Phloem,  114,  116. 

Photosynthesis,  186,  192,  193. 

Phototropism,  195. 

Phyllotaxy,  168,  169. 

Pileus,  373. 

Pinna,  402. 

Pinnate  veining,  172. 

Pinnule,  402. 

Pioneer  plant,  316,  319,  320. 

Pistil,  212,  214,  223,  228,  240. 

Pistillate,  267. 

Pitcher  plant,  209. 

Pith,  110,  115,  116,  119,  121,  122. 

Pitted  ducts,  114. 

Placenta,  216,  288,  298,  300. 

Plant  society,  316. 

Plasmolysis,  59. 

Pleurococcus,  337. 

Plicate,  155. 

Plumule,  11,  12,  14,  45,46. 

Pod,  298. 

Pollen,  213. 

Pollen  grains,  213. 

Pollen  sac,  213. 

Pollen  tubes,  249,  250. 

Pollination,  215,  247. 

Polycotyledons,  15,  45. 

Polymorphic,  365. 

Polymorphism,  365. 

Polypstalous,  211. 

Polyscpalous,  211. 

Pome,  2S8. 

Prefoliation,  1.55. 

Primary,  396. 

Primary  root,  42,  79. 

Pronuba,  278. 


INDEX 


373 


Protection,  199,  204,  207,  280,  287. 

Proteins,  3,  8,  33,  188,  204. 

Prothallium,  407. 

Protonema,  396. 

Protoplasm,  6,  7,  57,  58,  67.  110,  116. 

Pteridophytes,  335,  411,  412. 

Puccinia,  360. 

Pure  donjinant,  258,  259. 

Pure  forest,  139,  324. 

Pure  recessive,  258,  259. 

Pycnidia,  363. 

Quartered  cut,  135. 

Raceme,  161. 

Rhachis,  178. 

Radial  section,  132,  135. 

Radicle,  46. 

Rhaphe,  13. 

Ray,  161,  391. 

Ray  flowers,  231. 

Receptacle,  211,  288,  289,  388,  390,  398. 

Recessive,  257,  258. 

Red  rust,  359. 

Regular  flower,  219. 

Reproduction,  338,  351,  358,  383. 

Respiration,  30,  31,  191,  19 J. 

Resting  spore,  338,  342,  358,  394. 

Reticulation,  172,  402. 

Retrogressive  evolution,  418. 

Revolute,  373,  404. 

Rhizoids,  379,  386. 

Rhizome,  105. 

Ringing,  127. 

Rings  of  growth,  122,  123,  134,  135. 

Rogue,  260. 

Root  cap,  39. 

Root  hairs,  38,  67. 

Root  pressure,  Exp.  49. 

Root  pull,  69. 

Rootstock,  105. 

Root  system,  89. 

Root  tubercles,  63,  309. 

Rosette,  197. 

Rotation  of  crops,  24,  327. 

Runner,  95. 

Samara,  296. 

Sap  movement,  125,  120,  128,  129. 

Saprophyte,  86. 

Sap  wood,  131. 

Scale  leaves,  101,  106,  107,  147-149,  207. 

Scape,  107,  159. 

Scorpioid  inflorescence,  162  ;   Figs.    173- 

176. 
Screenings,  20 ;   p.  28,  Qn.  22. 
Secondary  roots,  37,  42,  79. 
Seed,  11-18,  332,  415. 


Seed  coat,  12,  14,  15,  43. 
Seedless  fruits,  285,  286. 
Seedlings,  36,  42,  43,  45. 
Seed  plants,  331,  414. 
Seed  vessel,  282. 
Selection,  260,  265,  2Sr). 

artificial,  262. 

natural,  261. 
Self-fertilization,  254,  271. 
Sepals,  211. 
Sessile,  167,  214. 
Seta,  399. 

Sexual  generation,  395,  396,  406,  410,  416. 
Sexual  reproduction,  394,  395,  410. 
Sheath,  67,  116. 
Shrinking  of  timber.  136. 
Sieve  tube,  114. 
Slabs,  134. 

Sleep  movements,  200. 
Soils,  75,  77. 
Sori,  404. 
Spathe,  221. 
Specialization,  237. 
Spermatophytes,  331,  335,  394,  414. 
Spermatozoid,  389. 
Spermogonia,  363. 
Spike,  161. 
Spirillum,  348. 
Spirogyra,  341. 
Sporangia,  390,  405. 
Spore,  332,  349,  .350.  377,  406,  410. 
Spore  case,  390,  393,  405. 
Spore  print,  376. 
Sporidium,  361. 
Sporogonium,  393,  399. 
Sporophyll,  406,  414. 
Sporophyte,  393-395,  399,  406,  410,  412, 

414,416. 
Sport,  264. 
Stamen,  212,  213. 
Staminate,  267,  268. 
Staminodia,  244. 
Standard,  238. 

Starch,  3,  4,  187,  204,  288;   Exps.  69,  70 
Stems,  90-99. 
Sterile  flower,  267. 
Sterilization,  354. 
Stigma,  214. 
Stigmatic  surface,  223, 
Stimulus,  98,  186,  201. 
Stipe,  240,  372,  402. 
Stipule,  149,  165,  166.      . 
Stolon,  95. 

Stoma,  181,  182,  183. 
Stomata,  181,  182. 
Stone  fruit,  292. 
Storage  of  food,  2,  3,  4,  17,  70,  103,  104- 

107,  287. 
Strangling  fig,  88. 


374 


INDEX 


Strobile,  411. 

Umbel,  161. 

Strobiliaceous,  411. 

Umbonate,  373. 

Style,  214. 

Underground  stems,  104-107 

Succession,  327. 

Unicellular,  337. 

Sugars,  3,  4,  204,  288. 

Unisexual,  267. 

Summer  spores,  360. 

Uredo,  359. 

Sundew,  210. 

Uredospore,  359,  360. 

Superior  ovary,  218.  221,  225. 

Supernumerary  buds,  158. 

Variation,  263,  264,  265. 

Suppressed,  220. 

Vascular  bundles.  111. 

Survival  of  the  fittest,  261. 

Vascular  cryptogams,  403,  411,  412 

Suture,  216,  298,  299. 

Vascular  cylinder,  64. 

Swarm  spore,  349. 

Vascular  system,  HI,  113,335. 

Swelling  of  timber,  136. 

Vegetative  reproduction,  358. 

Symbiosis,  309,  382. 

Veil,  371. 

Symmetrical  flower,  219. 

Veins,  173-176. 

Sympetalous,  211. 

Venter,  391. 

Syncarpous,  300. 

Ventral,  Figs.  390.  391. 

Synsepalous,  211. 

Vernation,  155. 

Systematic  botany,  see  Appendix. 

Vessels,  111. 

Vexillum,  238,  239. 

Tangential  cut,  132,  134. 

Vibrio,  348. 

Tap  root,  79. 

Vitality  of  seeds,  34;  Exp.  80. 

Teleutospore,  360. 

Volva,  371. 

Tendril,  96,  97. 

Terminal  bud,  145,  154. 

Water  roots,  39,  84. 

Testa,  14. 

Whorled  leaves,  168. 

Thallophytes,  333. 

Wind  pollination,  274,  275. 

Thallus,  333,  341,  343,  379.  380,  381,  385. 

Wings,  238, 

Tillage.  76. 

Winter  spores.  360. 

Tissue,  60,  61. 

Toadstools,  367. 

Xerophyte.  317. 

Toxins,  345. 

Xerophyte  societies,  317,  320-322. 

Tracheids.  114,  117. 

Xylem.  114,  116. 

Trailing,  95. 

Trama,  375. 

Yeast.  356. 

Transpiration,  179,  180. 

Yeast  colony.  357. 

Trifoliolate.  Figs.,  215'.  216. 

Yellow  trumpets,  209. 

Trimerous,  217. 

Yucca,  278. 

Trimorphic.  270. 

Yucca  moth,  278. 

Tuber,  106. 

Tumbleweeds.  23. 

Zonation,  325,  327. 

Turgidity,  7. 

bilateral,  326. 

Tiu-gor,  179. 

concentric,  326. 

Twining,  cause  of,  98;   Exp.  55. 

horizontal,  326. 

Twining  stems,  96  ;    Exp.  54. 

vertical,  326. 

Type,  18,  260,  263,  265,  336,  411. 

Zones  of  vegetation,  325 

■0  . 


PHOPEHTY  OF 


